Electromagnetic interference immune tissue invasive system

ABSTRACT

An electromagnetic immune tissue invasive system includes a primary device housing. The primary device housing having a control circuit therein. A shielding is formed around the primary device housing to shield the primary device housing and any circuits therein from electromagnetic interference. A lead system transmits and receives signals between the primary device housing. The lead system is either a fiber optic system or an electrically shielded electrical lead system.

PRIORITY INFORMATION

This application claims priority from U.S. Provisional PatentApplication, Serial No. 60/269,817, filed on Feb. 20, 2001; the entirecontents of which are hereby incorporated by reference.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

The subject matter of co-pending U.S. patent application Ser. No.09/885,867, filed on Jun. 20, 2001, entitled “Controllable, WearableMRI-Compatible Cardiac Pacemaker With Pulse Carrying Photonic CatheterAnd VOO Functionality”; co-pending U.S. patent application Ser. No.09/885,868, filed on Jun. 20, 2001, entitled “Controllable, WearableMRI-Compatible Cardiac Pacemaker With Power Carrying Photonic CatheterAnd VOO Functionality”; co-pending U.S. patent application Ser. No.10/037,513, filed on Jan. 4, 2002, entitled “Optical Pulse Generator ForBattery Powered Photonic Pacemakers And Other Light Driven MedicalStimulation Equipment”; co-pending U.S. patent application Ser. No.10/037,720, filed on Jan. 4, 2002, entitled “Opto-Electric CouplingDevice For Photonic Pacemakers And Other Opto-Electric MedicalStimulation Equipment”; co-pending U.S. patent application Ser. No.09/943,216, filed on Aug. 30, 2001, entitled “Pulse width Cardiac Pacingapparatus”; co-pending U.S. patent application Ser. No. 09/964,095,filed on Sep. 26, 2001, entitled “Process for Converting Light”; andco-pending U.S. patent application Ser. No. 09/921,066, filed on Aug. 2,2001, entitled “MRI-Resistant Implantable Device”. The entire contentsof each of the above noted co-pending U.S. patent applications (Ser.Nos.: 09/885,867; 09/885,868; 10/037,513; 10/037,720; 09/943,216;09/964,095; and 09/921,066) are hereby incorporated by reference.

FIELD OF THE PRESENT INVENTION

The present invention relates generally to an implantable device that isimmune or hardened to electromagnetic insult or interference. Moreparticularly, the present invention is directed to implantable systemsthat utilize fiber optic leads and other components to hardened orimmune the systems from electromagnetic insult, namelymagnetic-resonance imaging insult.

BACKGROUND OF THE PRESENT INVENTION

Magnetic resonance imaging (“MRI”) has been developed as an imagingtechnique adapted to obtain both images of anatomical features of humanpatients as well as some aspects of the functional activities ofbiological tissue. These images have medical diagnostic value indetermining the state of the health of the tissue examined.

In an MRI process, a patient is typically aligned to place the portionof the patient's anatomy to be examined in the imaging volume of the MRIapparatus. Such an MRI apparatus typically comprises a primary magnetfor supplying a constant magnetic field (B₀) which, by convention, isalong the z-axis and is substantially homogeneous over the imagingvolume and secondary magnets that can provide linear magnetic fieldgradients along each of three principal Cartesian axes in space(generally x, y, and z, or x₁, x₂ and x₃, respectively). A magneticfield gradient (ΔB₀/Δx_(i)) refers to the variation of the field alongthe direction parallel to B₀ with respect to each of the three principalCartesian axes, x_(i). The apparatus also comprises one or more RF(radio frequency) coils which provide excitation and detection of theMRI signal.

The use of the MRI process with patients who have implanted medicalassist devices; such as cardiac assist devices or implanted insulinpumps; often presents problems. As is known to those skilled in the art,implantable devices (such as implantable pulse generators (IPGs) andcardioverter/defibrillator/pacemakers (CDPs)) are sensitive to a varietyof forms of electromagnetic interference (EMI) because these enumerateddevices include sensing and logic systems that respond to low-levelelectrical signals emanating from the monitored tissue region of thepatient. Since the sensing systems and conductive elements of theseimplantable devices are responsive to changes in local electromagneticfields, the implanted devices are vulnerable to external sources ofsevere electromagnetic noise, and in particular, to electromagneticfields emitted during the magnetic resonance imaging (MRI) procedure.Thus, patients with implantable devices are generally advised not toundergo magnetic resonance imaging (MRI) procedures.

To more appreciate the problem, the use of implantable cardiac assistdevices during a MRI process will be briefly discussed.

The human heart may suffer from two classes of rhythmic disorders orarrhythmias: bradycardia and tachyarrhythmia. Bradycardia occurs whenthe heart beats too slowly, and may be treated by a common implantablepacemaker delivering low voltage (about 3 V) pacing pulses.

The common implantable pacemaker is usually contained within ahermetically sealed enclosure, in order to protect the operationalcomponents of the device from the harsh environment of the body, as wellas to protect the body from the device.

The common implantable pacemaker operates in conjunction with one ormore electrically conductive leads, adapted to conduct electricalstimulating pulses to sites within the patient's heart, and tocommunicate sensed signals from those sites back to the implanteddevice.

Furthermore, the common implantable pacemaker typically has a metal caseand a connector block mounted to the metal case that includesreceptacles for leads which may be used for electrical stimulation orwhich may be used for sensing of physiological signals. The battery andthe circuitry associated with the common implantable pacemaker arehermetically sealed within the case. Electrical interfaces are employedto connect the leads outside the metal case with the medical devicecircuitry and the battery inside the metal case.

Electrical interfaces serve the purpose of providing an electricalcircuit path extending from the interior of a hermetically sealed metalcase to an external point outside the case while maintaining thehermetic seal of the case. A conductive path is provided through theinterface by a conductive pin that is electrically insulated from thecase itself.

Such interfaces typically include a ferrule that permits attachment ofthe interface to the case, the conductive pin, and a hermetic glass orceramic seal that supports the pin within the ferrule and isolates thepin from the metal case.

A common implantable pacemaker can, under some circumstances, besusceptible to electrical interference such that the desiredfunctionality of the pacemaker is impaired. For example, commonimplantable pacemaker requires protection against electricalinterference from electromagnetic interference (EMI), defibrillationpulses, electrostatic discharge, or other generally large voltages orcurrents generated by other devices external to the medical device. Asnoted above, more recently, it has become crucial that cardiac assistsystems be protected from magnetic-resonance imaging sources.

Such electrical interference can damage the circuitry of the cardiacassist systems or cause interference in the proper operation orfunctionality of the cardiac assist systems. For example, damage mayoccur due to high voltages or excessive currents introduced into thecardiac assist system.

Therefore, it is required that such voltages and currents be limited atthe input of such cardiac assist systems, e.g., at the interface.Protection from such voltages and currents has typically been providedat the input of a cardiac assist system by the use of one or more zenerdiodes and one or more filter capacitors.

For example, one or more zener diodes may be connected between thecircuitry to be protected, e.g., pacemaker circuitry, and the metal caseof the medical device in a manner which grounds voltage surges andcurrent surges through the diode(s). Such zener diodes and capacitorsused for such applications may be in the form of discrete componentsmounted relative to circuitry at the input of a connector block wherevarious leads are connected to the implantable medical device, e.g., atthe interfaces for such leads.

However, such protection, provided by zener diodes and capacitors placedat the input of the medical device, increases the congestion of themedical device circuits, at least one zener diode and one capacitor perinput/output connection or interface. This is contrary to the desire forincreased miniaturization of implantable medical devices.

Further, when such protection is provided, interconnect wire length forconnecting such protection circuitry and pins of the interfaces to themedical device circuitry that performs desired functions for the medicaldevice tends to be undesirably long. The excessive wire length may leadto signal loss and undesirable inductive effects. The wire length canalso act as an antenna that conducts undesirable electrical interferencesignals to sensitive CMOS circuits within the medical device to beprotected.

Additionally, the radio frequency (RF) energy that is inductivelycoupled into the wire causes intense heating along the length of thewire, and at the electrodes that are attached to the heart wall. Thisheating may be sufficient to ablate the interior surface of the bloodvessel through which the wire lead is placed, and may be sufficient tocause scarring at the point where the electrodes contact the heart. Afurther result of this ablation and scarring is that the sensitive nodethat the electrode is intended to pace with low voltage signals becomesdesensitized, so that pacing the patient's heart becomes less reliable,and in some cases fails altogether.

Another conventional solution for protecting the implantable medicaldevice from electromagnetic interference is illustrated in FIG. 1. FIG.1 is a schematic view of an implantable medical device 12 embodyingprotection against electrical interference. At least one lead 14 isconnected to the implantable medical device 12 in connector block region13 using an interface.

In the case where implantable medical device 12 is a pacemaker implantedin a body 10, the pacemaker 12 includes at least one or both of pacingand sensing leads represented generally as leads 14 to sense electricalsignals attendant to the depolarization and repolarization of the heart16, and to provide pacing pulses for causing depolarization of cardiactissue in the vicinity of the distal ends thereof.

FIG. 2 more particularly illustrates the circuit that is usedconventionally to protect from electromagnetic interference. As shown inFIG. 2, protection circuitry 15 is provided using a diode arraycomponent 30. The diode array consists of five zener diode triggeredsemiconductor controlled rectifiers (SCRs) with anti-parallel diodesarranged in an array with one common connection. This allows for a smallfootprint despite the large currents that may be carried through thedevice during defibrillation, e.g., 10 amps. The SCRs 20-24 turn on andlimit the voltage across the device when excessive voltage and currentsurges occur.

As shown in FIG. 2, each of the zener diode triggered SCRs 20-24 isconnected to an electrically conductive pin 25, 26, 28, 29,respectively. Further, each electrically conductive pin 25, 26, 28, 29is connected to a medical device contact region 31, 32, 34, 35 to bewire bonded to pads of a printed circuit board. The diode arraycomponent 30 is connected to the electrically conductive pins 25, 26,28, 29 via the die contact regions, respectively, along with otherelectrical conductive traces of the printed circuit board.

Other attempts have been made to protect implantable devices from MRIfields. For example, U.S. Pat. No. 5,968,083 (to Ciciarelli et al.)describes a device adapted to switch between low and high impedancemodes of operation in response to EMI insult. Furthermore, U.S. Pat. No.6,188,926 (to Vock) discloses a control unit for adjusting a cardiacpacing rate of a pacing unit to an interference backup rate when heartactivity cannot be sensed due to EMI.

Although, conventional medical devices provide some means for protectionagainst electromagnetic interference, these conventional devices requiremuch circuitry and fail to provide fail-safe protection againstradiation produced by magnetic-resonance imaging procedures. Moreover,the conventional devices fail to address the possible damage that can bedone at the tissue interface due to RF-induced heating, and they fail toaddress the unwanted heart stimulation that may result from RF-inducedelectrical currents.

Thus, it is desirable to provide protection against electromagneticinterference, without requiring much circuitry and to provide fail-safeprotection against radiation produced by magnetic-resonance imagingprocedures. Moreover, it is desirable to provide devices that preventthe possible damage that can be done at the tissue interface due toinduced electrical signals and due to thermal tissue damage.Furthermore, it is desirable to provide to provide an effective meansfor transferring energy from one point in the body to another pointwithout having the energy causing a detrimental effect upon the body.

SUMMARY OF THE PRESENT INVENTION

A first aspect of the present invention is a cardiac assist system. Thecardiac assist system includes a primary device housing; the primarydevice housing having a control circuit therein; a shielding formedaround the primary device housing to shield the primary device housingand any circuits therein from electromagnetic interference; and a leadsystem to transmit and receive signals between a heart and the primarydevice housing.

A second aspect of the present invention is a cardiac assist system. Thecardiac assist system includes a primary device housing; the primarydevice housing having a control circuit therein; a lead system totransmit and receive signals between a heart and the primary devicehousing; and a detection circuit, located in the primary device housing,to detect an electromagnetic interference insult upon the cardiac assistsystem. The control circuit places the cardiac assist system in anasynchronous mode upon detection of the electromagnetic interferenceinsult by the detection system.

A third aspect of the present invention is a cardiac assist system. Thecardiac assist system includes a primary device housing; the primarydevice housing having a control circuit therein; a shielding formedaround the primary device housing to shield the primary device housingand any circuits therein from electromagnetic interference; a fiberoptic based lead system to receive signals at the primary housing from aheart; and an electrical based lead system to transmit signals to theheart from the primary device housing.

A fourth aspect of the present invention is a cardiac assist system. Thecardiac assist system includes a primary device housing; the primarydevice housing having a control circuit therein; a shielding formedaround the primary device housing to shield the primary device housingand any circuits therein from electromagnetic interference; and a fiberoptic based lead system to receive signals at the primary housing from aheart and to transmit signals to the heart from the primary devicehousing.

A fifth aspect of the present invention is a cardiac assist system forimplanting in a body of a patient, the cardiac assist system comprising;a main module; a magnetic-resonance imaging-immune auxiliary module; acommunication channel between the main module and the magnetic-resonanceimaging-immune auxiliary module for the magnetic-resonanceimaging-immune auxiliary module to detect failure of the main module;and a controller for activating the magnetic-resonance imaging-immuneauxiliary module upon detection of failure of the main module.

A sixth aspect of the present invention is a cardiac assist system. Thecardiac assist system includes a primary device housing including apower supply and a light source; the primary device housing having acontrol circuit therein; a shielding formed around the primary devicehousing to shield the primary device housing and any circuits thereinfrom electromagnetic interference; a cardiac assist device associatedwith a heart; and a photonic lead system to transmit between the primarydevice housing and the cardiac assist device, both power and controlsignals in the form of light.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system includes a primary device housing; the primarydevice housing having a first control circuit, therein, to performsynchronous cardiac assist operations; a secondary device housing havinga second control circuit therein, to perform asynchronous cardiac assistoperations; and a detection circuit, communicatively coupled to thefirst and second control circuits, to detect an electromagneticinterference insult upon the cardiac assist system. The first controlcircuit terminates synchronous cardiac assist operations and the secondcontrol circuit initiates asynchronous cardiac assist operations upondetection of the electromagnetic interference insult by the detectionsystem.

A further aspect of the present invention is an implantable cable fortransmission of a signal to and from a body tissue of a vertebrate. Theimplantable cable includes a fiber optic bundle having a surface ofnon-immunogenic, physiologically compatible material, the fiber opticbundle being capable of being permanently implanted in a body cavity orsubcutaneously, the fiber optic bundle having a distal end forimplantation at or adjacent to the body tissue and a proximal end. Theproximal end is adapted to couple to and direct an optical signalsource; the distal end is adapted to couple to an optical stimulator.The fiber optic bundle delivers an optical signal intended to cause anoptical simulator located at the distal end to deliver an excitatorystimulus to a selected body tissue, the stimulus being causing theselected body tissue to function as desired.

A further aspect of the present invention is an implantable cable fortransmission of a signal to and from a body tissue of a vertebrate. Theimplantable cable includes a fiber optic bundle having a surface ofnon-immunogenic, physiologically compatible material, the fiber opticbundle being capable of being permanently implanted in a body cavity orsubcutaneously, the fiber optic bundle having a distal end forimplantation at or adjacent to the body tissue and a proximal end. Theproximal end is adapted to couple to an optical signal receiver, thedistal end is adapted to couple to a sensor; the fiber optic bundledelivers an optical signal from a coupled sensor intended to cause anoptical signal receiver coupled to the proximal end to monitorcharacteristics of a selected body tissue.

A further aspect of the present invention is an implantable cable fortransmission of power to a body tissue of a vertebrate. The implantablecable consists of a fiber optic lead having a surface ofnon-immunogenic, physiologically compatible material and being capableof being permanently implanted in a body cavity or subcutaneously. Thefiber optic lead has a proximal end adapted to couple to an opticalportal, a coupled optical portal being able to receive light from asource external to the vertebrate, and a distal end adapted to couple toa photoelectric receiver, a coupled photoelectric receiver being able toconvert light into electrical energy for use at the distal end.

A further aspect of the present invention is an implantable cable forthe transmission of power to a body tissue of a vertebrate. Theimplantable cable consists of a fiber optic lead having a surface ofnon-immunogenic, physiologically compatible material and being capableof being permanently implanted in a body cavity or subcutaneously. Thefiber optic lead has a distal end adapted to couple to a sensor, acoupled sensor being able to produce light signal based on a measuredcharacteristic of a selected body tissue region, and a proximal endbeing adapted to couple to an optical portal, the optical portal beingable to receive light produced by a coupled sensor.

A further aspect of the present invention is an implantable cable forthe transmission of power to a body tissue of a vertebrate. Theimplantable cable consists of a fiber optic lead having a surface ofnon-immunogenic, physiologically compatible material and being capableof being permanently implanted in a body cavity or subcutaneously. Thefiber optic lead has a proximal end being adapted to be coupled to anoptical portal, a coupled optical portal being able to receive lightfrom a light source, and a distal end being adapted to be coupled to aphotoelectric receiver, a coupled photoelectric receiver being able toconvert light into electrical energy for use at the distal end.

A further aspect of the present invention is an implantable cable forthe transmission of power to a body tissue of a vertebrate. Theimplantable cable includes a fiber optic lead having a cylindricalsurface of non-immunogenic, physiologically compatible material andbeing capable of being permanently implanted in a body cavity orsubcutaneously. The fiber optic lead has a proximal end coupled to anelectro-optical source; the electro-optical source converts electricalenergy into light energy. The distal end coupled to a photoelectricreceiver, the photoelectric receiver converts light energy intoelectrical energy for use at the distal end.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system includes a primary device housing, having acontrol circuit therein, and a fiber optic based communication system totransmit and receive signals between a desired anatomical cardiac tissueregion and the primary device housing.

A still further aspect of the present invention is a tissue invasivedevice. The tissue invasive device includes a primary device housing,having a control circuit therein and a fiber optic based communicationsystem to transmit and receive signals between a selected tissue regionand the primary device housing.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system includes a primary device housing, having acontrol circuit therein, and a lead system to transmit and receivesignals between a desired anatomical cardiac tissue region and theprimary device housing. The lead system includes a sensing andstimulation system at an epicardial-lead interface with the desiredanatomical cardiac tissue region. The sensing and stimulation systemincludes optical sensing components to detect physiological signals fromthe desired anatomical cardiac tissue region.

A still further aspect of the present invention is a tissue invasivedevice. The tissue invasive device includes a primary device housing,having a control circuit therein, and a lead system to transmit andreceive signals between a selected tissue region and the primary devicehousing. The lead system includes a sensing and stimulation system at aninterface with the selected tissue region. The sensing and stimulationsystem includes optical sensing components to detect physiologicalsignals from the selected tissue region.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system consists of a primary device housing, having acontrol circuit therein, and a lead system to transmit and receivesignals between a desired anatomical cardiac tissue region and theprimary device housing. The lead system includes a sensing andstimulation system at an epicardial-lead interface with the desiredanatomical cardiac tissue region; the sensing and stimulation systemincludes optical sensing components to detect physiological signals fromthe desired anatomical cardiac tissue region and electrical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

A still further aspect of the present invention is a tissue invasivedevice. The tissue invasive device includes a primary device housing,having a control circuit therein, and a lead system to transmit andreceive signals between a selected tissue region and the primary devicehousing. The lead system includes a sensing and stimulation system at anepicardial-lead interface with the selected tissue region. The sensingand stimulation system includes optical sensing components to detectphysiological signals from the selected tissue region and electricalsensing components to detect physiological signals from the selectedtissue region.

A further aspect of the present invention is a transducer system totransmit and receive signals between a selected tissue region and atissue invasive device. The transducer system consists of an electricallead and an electrode located on an end of the electrical lead having ananti-antenna geometrical shape, the anti-antenna geometrical shapepreventing the electrode from picking up and conducting strayelectromagnetic interference.

A further aspect of the present invention is a cardiac assist transducersystem to transmit and receive signals between a cardiac tissue regionand a cardiac assist device. The cardiac assist transducer systemconsists of an electrical lead to deliver electrical pulses to thecardiac tissue region; and an electrode located on an end of theelectrical lead having an anti-antenna geometrical shape, theanti-antenna geometrical shape preventing the electrode from picking upand conducting stray electromagnetic interference.

A still further aspect of the present invention is a cardiac assistsystem. The cardiac assist system consists of a primary device housing;the primary device housing has a control circuit therein; a lead systemto transmit and receive signals between a heart and the primary devicehousing; a shielding formed around the lead system to shield the leadsystem from electromagnetic interference; and a biocompatible materialformed around the shielding.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system consists of a primary device housing; theprimary device housing has a control circuit therein; a fiber opticEMI-immune lead system to transmit and receive signals between a heartand the primary device housing; and a biocompatible material formedaround the fiber optic EMI-immune lead system.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system consists of a primary device housing; theprimary device housing has a control circuit therein; anoptical-electrical lead system to transmit and receive signals between aheart and the primary device housing; a shielding formed around theoptical-electrical lead system to shield the optical-electrical leadsystem from electromagnetic interference; and a biocompatible materialformed around the shielding.

A further aspect of the present invention is a tissue invasive device.The tissue invasive device consists of a primary device housing; theprimary device housing has a control circuit therein; a lead system totransmit and receive signals between a selected tissue region and theprimary device housing; a shielding formed around the lead system toshield the lead system from electromagnetic interference; and abiocompatible material formed around the shielding.

A still further aspect of the present invention is a tissue invasivedevice. The tissue invasive device consists of a primary device housing;the primary device housing having a control circuit therein; a fiberoptic EMI-immune lead system to transmit and receive signals between aselected tissue region and the primary device housing; and abiocompatible material formed around the fiber optic EMI-immune leadsystem.

A further aspect of the present invention is a tissue invasive device.The tissue invasive device consists of a primary device housing; theprimary device housing having a control circuit therein; anoptical-electrical lead system to transmit and receive signals between aselected tissue region and the primary device housing; a shieldingformed around the optical-electrical lead system to shield theoptical-electrical lead system from electromagnetic interference; and abiocompatible material formed around the shielding.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system consists of a primary device housing; theprimary device housing has a control circuit therein; a shielding formedaround the primary device housing to shield the primary device housingand any circuits therein from electromagnetic interference; and abiocompatible material formed around the shielding.

A further aspect of the present invention is a tissue invasive device.The tissue invasive device consists of a primary device housing; theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; anda biocompatible material formed around the shielding.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system consists of a primary device housing; theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; abiocompatible material formed around the shielding; and a detectioncircuit, located in the primary device housing, to detect anelectromagnetic interference insult upon the cardiac assist system. Thecontrol circuit will place the cardiac assist system in an asynchronousmode upon detection of the electromagnetic interference insult by thedetection system.

A still further aspect of the present invention is a tissue invasivedevice. The tissue invasive device consists of a primary device housing;the primary device housing has a control circuit therein operating in afirst mode. A shielding formed around the primary device housing toshield the primary device housing and any circuits therein fromelectromagnetic interference; a biocompatible material formed around theshielding; and a detection circuit, located in the primary devicehousing, to detect an electromagnetic interference insult upon thetissue invasive device. The control circuit places the tissue invasivedevice in a second mode upon detection of the electromagneticinterference insult by the detection system.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system consists of a primary device housing having afirst control circuit, therein, to perform synchronous cardiac assistoperations; a first shielding formed around the primary device housingto shield the primary device housing and any circuits therein fromelectromagnetic interference; a first biocompatible material formedaround the first shielding; a secondary device housing having a secondcontrol circuit, therein, to perform asynchronous cardiac assistoperations; a second shielding formed around the secondary devicehousing to shield the secondary device housing and any circuits thereinfrom electromagnetic interference; a second biocompatible materialformed around the second shielding; and a detection circuit,communicatively coupled to the first and second control circuits, todetect an electromagnetic interference insult upon the cardiac assistsystem. The first control circuit terminates synchronous cardiac assistoperations and the second control circuit initiates asynchronous cardiacassist operations upon detection of the electromagnetic interferenceinsult by the detection system.

A still further aspect of the present invention is a cardiac assistsystem for implanting in a body of a patient. The cardiac assist systemconsists of a main module; a first shielding formed around the mainmodule to shield the main module and any circuits therein frommagnetic-resonance imaging interference; a first biocompatible materialformed around the first shielding; a magnetic-resonance imaging-immuneauxiliary module; a second shielding formed around themagnetic-resonance imaging-immune auxiliary module to shield themagnetic-resonance imaging-immune auxiliary module and any circuitstherein from magnetic-resonance imaging interference; a secondbiocompatible material formed around the second shielding; acommunication channel between the main module and the magnetic-resonanceimaging-immune auxiliary module for the magnetic-resonanceimaging-immune auxiliary module to detect failure of the main module;and a controller for activating the magnetic-resonance imaging-immuneauxiliary module upon detection of failure of the main module.

A further aspect of the present invention is a cardiac assist system forimplanting in the body of a patient. The cardiac assist system consistsof a main module; a first biocompatible material formed around the mainmodule; an magnetic-resonance imaging-hardened auxiliary module; ashielding formed around the magnetic-resonance imaging-hardenedauxiliary module to shield the magnetic-resonance imaging-hardenedauxiliary module and any circuits therein from magnetic-resonanceimaging interference; a second biocompatible material formed around thesecond shielding; and a communication channel between the main moduleand the magnetic-resonance imaging-hardened auxiliary module. Themagnetic-resonance imaging-hardened auxiliary module detecting, throughthe communication channel, failure of the main module; themagnetic-resonance imaging-hardened auxiliary module including acontroller for activating the magnetic-resonance imaging-hardenedauxiliary module upon detection of failure of the main module.

A further aspect of the present invention is a cardiac assist device.The cardiac assist device consists of a primary device housing; theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; alead system to transmit and receive signals between a selected cardiactissue region and the primary device housing; a switch to place thecontrol circuitry into a fixed-rate mode of operation; an acousticsensor to sense a predetermined acoustic signal. The switch places thecontrol circuitry into a fixed-rate mode of operation when the acousticsensor senses the predetermined acoustic signal.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system includes a primary device housing; the primarydevice housing having a control circuit therein; a shielding formedaround the primary device housing to shield the primary device housingand any circuits therein from electromagnetic interference; a leadsystem to transmit and receive signals between a selected cardiac tissueregion and the primary device housing; a switch to place the controlcircuitry into a fixed-rate mode of operation; a near infrared sensor tosense a predetermined near infrared signal; the switch placing thecontrol circuitry into a fixed-rate mode of operations when the nearinfrared sensor senses the predetermined near infrared signal.

A still further aspect of the present invention is an implantable cablefor the transmission of signals to and from a body tissue of avertebrate. The implantable cable consists of a fiber optic lead havinga surface of non-immunogenic, physiologically compatible material andbeing capable of being permanently implanted in a body cavity orsubcutaneously; the fiber optic lead having a distal end forimplantation at or adjacent to the body tissue and a proximal end; thefiber optic lead including a first optical fiber and a second opticalfiber; the first optical fiber having, a proximal end coupled to anoptical signal source, and a distal end coupled to an opticalstimulator. The optical signal source generating an optical signalintended to cause the optical stimulator located at a distal end todeliver an excitatory stimulus to a selected body tissue, the stimuluscausing the selected body tissue to function as desired. The secondoptical fiber having a distal end coupled to a sensor, and a proximalend coupled to a device responsive to an optical signal delivered by thesecond optical fiber; the sensor generating an optical signal torepresent a state of a function of the selected body tissue to providefeedback to affect the activity of the optical signal source.

A further aspect of the present invention is an implantable cable forthe transmission of signals to and from a body tissue of a vertebrate.The implantable cable includes a fiber optic lead having a surface ofnon-immunogenic, physiologically compatible material and being capableof being permanently implanted in a body cavity or subcutaneously; thefiber optic lead having a distal end for implantation at or adjacent tothe body tissue and a proximal end; the proximal end of the fiber opticlead being coupled to an optical signal source and an optical device.The distal end of the fiber optic lead being coupled to an opticalstimulator and a sensor; the optical signal source generating an opticalsignal intended to cause the optical stimulator located at a distal endto deliver an excitatory stimulus to a selected body tissue, thestimulus being causing the selected body tissue to function as desired.The optical device being responsive to an optical signal generated bythe sensor, the optical signal generated by the sensor rep representinga state of a function of the selected body tissue to provide feedback toaffect the activity of the optical signal source.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system includes a primary device housing including apower supply and a light source; the primary device housing having acontrol circuit therein; a shielding formed around the primary devicehousing to shield the primary device housing and any circuits thereinfrom electromagnetic interference; a cardiac assist device associatedwith a heart; a photonic lead system to transmit between the primarydevice housing and the cardiac assist device, both power and controlsignals in the form of light; a photoresponsive device to convert thelight transmitted by the photonic lead system into electrical energy andto sense variations in the light energy to produce control signals; acharge accumulating device to receive and store the electrical energyproduced by the photoresponsive device; and a discharge control device,responsive to the control signals, to direct the stored electricalenergy from the charge accumulating device to the cardiac assist deviceassociated with the heart.

A further aspect of the present invention is a tissue implantabledevice. The tissue implantable device includes a primary device housingincluding a power supply and a light source; the primary device housinghaving a control circuit therein; a shielding formed around the primarydevice housing to shield the primary device housing and any circuitstherein from electromagnetic interference; a tissue interface deviceassociated with a distinct tissue region; a photonic lead system totransmit between the primary device housing and the tissue interfacedevice, both power and control signals in the form of light; aphotoresponsive device to convert the light transmitted by the photoniclead system into electrical energy and to sense variations in the lightenergy to produce control signals; a discharge control device,responsive to the control signals, to direct the stored electricalenergy from the charge accumulating device to the tissue interfacedevice associated with a distinct tissue region.

A further aspect of the present invention is a tissue implantabledevice. The tissue implantable device includes a primary device housing;the primary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; alead system to transmit and receive signals between a tissue region ofconcern and the primary device housing; and a detection circuit todetect a phase timing of an external electromagnetic field; the controlcircuit altering its operations to avoid interfering with the detectedexternal electromagnetic field.

A still further aspect of the present invention is a method forpreventing a tissue implantable device failure during magnetic resonanceimaging. The method includes determining a quiet period for a tissueimplantable device and generating a magnetic resonance imaging pulseduring a quiet period of the tissue implantable device.

A further aspect of the present invention is a method for preventing atissue implantable device failure due to an external electromagneticfield source. The method includes detecting a phase timing of anexternal electromagnetic field and altering operations of the tissueimplantable device to avoid interfering with the detected externalelectromagnetic field.

A further aspect of the present invention is a method for preventing atissue implantable device failure during magnetic resonance imaging. Themethod includes detecting a phase timing of an external magneticresonance imaging pulse field and altering operations of the tissueimplantable device to avoid interfering with the detected externalmagnetic resonance imaging pulse field.

A further aspect of the present invention is a cardiac assist system forimplanting in the body of a patient. The cardiac assist system includesa main module; an magnetic-resonance imaging-hardened auxiliary module;and a communication channel between the main module and themagnetic-resonance imaging-hardened auxiliary module; themagnetic-resonance imaging-hardened auxiliary module detecting, throughthe communication channel, failure of the main module; themagnetic-resonance imaging-hardened auxiliary module including acontroller for activating the auxiliary module upon detection of failureof the main module.

A further aspect of the present invention is a signaling system for atwo-module implantable medical device having a main module and anauxiliary module. The signaling system consists of signaling means inthe main module for generating a signal to the auxiliary module, thesignal representing a status of the main module or an instruction forthe auxiliary module to activate; sensing means in the auxiliary module,in response to the signal from the signaling means, for determining ifthe auxiliary module should activate; and a switch to activate theauxiliary module when the sensing means determines that the signal fromthe signaling means indicates that the auxiliary module should activate.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system includes a primary device housing; the primarydevice housing having a control circuit therein; a shielding formedaround the primary device housing to shield the primary device housingand any circuits therein from electromagnetic interference; and a leadsystem to transmit and receive signals between a heart and the primarydevice housing; the control circuitry including an oscillator andamplifier operating at an amplitude level above that of an inducedsignal from a magnetic-resonance imaging field.

A still further aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing; theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; alead system to transmit and receive signals between a heart and theprimary device housing; a switch to place the control circuitry into afixed-rate mode of operation; a changing magnetic field sensor to sensea change in magnetic field around the primary housing, the switchplacing the control circuitry into a fixed-rate mode of operation whenthe changing magnetic field sensor senses a predetermined encodedchanging magnetic field.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive delivery system. The electromagneticradiation immune tissue invasive delivery system includes a photoniclead having a proximal end and a distal end; a storage device, locatedat the proximal end of the photonic lead, to store a therapeuticsubstance to be introduced into a tissue region; a delivery device todelivery a portion of the stored therapeutic substance to a tissueregion; a light source, in the proximal end of the photonic lead, toproduce a first light having a first wavelength and a second lighthaving a second wavelength; a wave-guide between the proximal end anddistal end of the photonic lead; a bio-sensor, in the distal end of thephotonic lead, to sense characteristics of a predetermined tissueregion; a distal sensor, in the distal end of the photonic lead, toconvert the first light into electrical energy and, responsive to thebio-sensor, to reflect the second light back the proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region; a proximal sensor, in the proximal end of the photoniclead, to convert the modulated second light into electrical energy; anda control circuit, in response to the electrical energy from theproximal sensor, to control an amount of the stored therapeuticsubstance to be introduced into the tissue region.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive delivery system. The electromagneticradiation immune tissue invasive delivery system includes a photoniclead having a proximal end and a distal end; a storage device, locatedat the proximal end of the photonic lead, to store a therapeuticsubstance to be introduced into a tissue region; a delivery device todeliver a portion of the stored therapeutic substance to a tissueregion; a light source, in the proximal end of the photonic lead, toproduce a first light having a first wavelength and a second lighthaving a second wavelength; a wave-guide between the proximal end anddistal end of the photonic lead; a bio-sensor, in the distal end of thephotonic lead, to sense characteristics of a predetermined tissueregion; a distal sensor, in the distal end of the photonic lead, toconvert the first light into electrical energy and, responsive to thebio-sensor, to emit a second light having a second wavelength toproximal end of the photonic lead such that a characteristic of thesecond light is modulated to encode the sensed characteristics of thepredetermined tissue region; a proximal sensor, in the proximal end ofthe photonic lead, to convert the modulated second light into electricalenergy; and a control circuit, in response to the electrical energy fromthe proximal sensor, to control an amount of the stored therapeuticsubstance to be introduced into the tissue region.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive stimulation system. The electromagneticradiation immune tissue invasive stimulation system includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength; a wave-guide between the proximal end and distal endof the photonic lead; a distal sensor, in the distal end of the photoniclead, to convert the first light into electrical energy into controlsignals; an electrical energy storage device to store electrical energy;and a control circuit, in response to the control signals, to cause aportion of the stored electrical energy to be delivered to apredetermined tissue region.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive sensing system. The electromagneticradiation immune tissue invasive sensing system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength; a wave-guide between the proximal end and distal end of thephotonic lead; a distal sensor, in the distal end of the photonic lead,to convert the first light into electrical energy into control signals;an electrical energy storage device to store electrical energy; and abio-sensor, in the distal end of the photonic lead, to sense acharacteristic of a predetermined tissue region. The light source, inthe proximal end of the photonic lead, produces a second light having asecond wavelength. The distal sensor, in the distal end of the photoniclead and responsive to the bio-sensor, reflects the second light backthe proximal end of the photonic lead such that a characteristic of thesecond light is modulated to encode the sensed characteristic of thepredetermined tissue region.

A still further aspect of the present invention is an electromagneticradiation immune tissue invasive sensing system. The electromagneticradiation immune tissue invasive sensing system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength and a second light having a second wavelength; a wave-guidebetween the proximal end and the distal end of the photonic lead; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; and a distal sensor,in the distal end of the photonic lead, to convert the first light intoelectrical energy and, responsive to the bio-sensor, to reflect thesecond light back the proximal end of the photonic lead such that acharacteristic of the second light is modulated to encode the sensedcharacteristics of the predetermined tissue region.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive sensing system. The electromagneticradiation immune tissue invasive sensing system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength; a wave-guide between the proximal end and distal end of thephotonic lead; a bio-sensor, in the distal end of the photonic lead, tosense characteristics of a predetermined tissue region; and a distalsensor, in the distal end of the photonic lead, to convert the firstlight into electrical energy and, responsive to the bio-sensor, to emita second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region.

A further aspect of the present invention is a photonic lead system. Thephotonic lead system includes a photonic lead having a distal end and aproximal end; and a magnetic radiation coil, located in the distal end,to detect characteristics of magnetic radiation of a predeterminednature.

A still further aspect of the present invention is an electromagneticradiation immune sensing system. The electromagnetic radiation immunesensing system includes a photonic lead having a proximal end and adistal end; a light source, in the proximal end of the photonic lead, toproduce a first light having a first wavelength and a second lighthaving a second wavelength; a wave-guide between the proximal end anddistal end of the photonic lead; a biosensor, in the distal end of thephotonic lead, to measure changes in an electric field located outside abody, the electric field being generated by the shifting voltages on abody's skin surface; and a distal sensor, in the distal end of thephotonic lead, to convert the first light into electrical energy and,responsive to the bio-sensor, to reflect the second light back theproximal end of the photonic lead such that a characteristic of thesecond light is modulated to encode the measured changes in the electricfield.

A further aspect of the present invention is an electromagneticradiation immune sensing system. The electromagnetic radiation immunesensing system includes a photonic lead having a proximal end and adistal end; a light source, in the proximal end of the photonic lead, toproduce a first light having a first wavelength; a wave-guide betweenthe proximal end and distal end of the photonic lead; a bio-sensor, inthe distal end of the photonic lead, to measure changes in an electricfield located outside a body, the electric field being generated by theshifting voltages on a body's skin surface; and a distal sensor, in thedistal end of the photonic lead, to convert the first light intoelectrical energy and, responsive to the bio-sensor, to emit a secondlight having a second wavelength to proximal end of the photonic leadsuch that a characteristic of the second light is modulated to encodethe measured changes in the electric field.

A further aspect of the present invention is a cardiac assist system.The cardiac assist system includes a primary device housing, the primarydevice housing having a control circuit therein; a shielding formedaround the primary device housing to shield the primary device housingand any circuits therein from electromagnetic interference; a leadsystem to transmit and receive signals between a heart and the primarydevice housing; a switch to place the control circuitry into afixed-rate mode of operation; and a changing magnetic field sensor tosense a change in magnetic field around the primary housing. The switchcauses the control circuitry to turn-off and cease operation when thechanging magnetic field sensor senses a predetermined encoded changingmagnetic field.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; a radiationscattering medium at the distal end of the photonic lead to receiveradiation from the wave-guide; and a plurality of sensors to receivescattered radiation from the radiation scattering medium and convert thereceived scattered radiation into electrical energy.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a first wave-guidebetween the proximal end and distal end of the photonic lead; a secondwave-guide, having a plurality of beam splitters therein at the distalend of the photonic lead to receive radiation from the first wave-guide;and a plurality of sensors to receive radiation from the beam splittersin the second wave-guide and convert the received radiation intoelectrical energy.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; and a plurality ofstacked sensors to receive radiation from the wave-guide and convert thereceived radiation into electrical energy. Each sensor absorbs afraction of radiation incident upon the stack of sensors.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; and a plurality ofconcentric sensors to receive radiation from the wave-guide and convertthe received radiation into electrical energy. Each concentric sensorsabsorbs a fraction of radiation from said wave-guide.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; a sensor toreceive radiation from the wave-guide and convert the received radiationinto electrical energy; and a plurality of switchable capacitorsconnected in parallel to an output of the sensor to enable simultaneouscharging of the capacitors.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; a sensor toreceive radiation from the wave-guide and convert the received radiationinto electrical energy; a control circuit connected to an output of thesensor; and a plurality of switchable capacitors connected to thecontrol circuit.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; a sensor toreceive radiation from the wave-guide and convert the received radiationinto electrical energy; and a plurality of switchable capacitorsconnected to an output of the sensor to enable sequential charging ofthe capacitors with a pre-determined pulse intensity and duration.

A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a light source; a radiation beam splitter having multiple beamsplitters; a plurality of wave-guides, each wave-guide receivingradiation from a beam splitter; and a plurality of sensors, each sensorreceiving radiation from one of the plurality of wave-guides to convertthe received radiation into electrical energy.

A further aspect of the present invention is a tissue invasive photonicsystem. The tissue invasive photonic system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength and a second light having a second wavelength; a wave-guidebetween the proximal end and distal end of the photonic lead; aradiation scattering medium at the distal end of the photonic lead toreceive radiation from the wave-guide; a plurality of power sensors toreceive scattered radiation from the radiation scattering medium andconvert the received scattered radiation into electrical energy; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; and a distal emitter,in the distal end of the photonic lead and responsive to the bio-sensor,to emit a second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region.

A further aspect of the present invention is a tissue invasive photonicsystem. The tissue invasive photonic system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength and a second light having a second wavelength; a firstwave-guide between the proximal end and distal end of the photonic lead;a second wave-guide, having a plurality of power beam splitters thereinat the distal end of the photonic lead to receive and reflect the firstlight from the first wave-guide; a plurality of power sensors to receivethe first light from the power beam splitters in the second wave-guideand convert the received first light into electrical energy; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; and a distal emitter,in the distal end of the photonic lead and responsive to the bio-sensor,to emit a second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region.

A further aspect of the present invention is a tissue invasive photonicsystem. The tissue invasive photonic system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength and a second light having a second wavelength; a wave-guidebetween the proximal end and distal end of the photonic lead; aplurality of power sensors to receive the first light from thewave-guide and convert the received first light into electrical energy,each power sensor absorbing a fraction of the received first light; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; and a distal emitter,in the distal end of the photonic lead and responsive to the bio-sensor,to emit a second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region.

A further aspect of the present invention is a tissue invasive photonicsystem. The tissue invasive photonic system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength and a second light having a second wavelength; a wave-guidebetween the proximal end and distal end of the photonic lead; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; a distal emitter, inthe distal end of the photonic lead and responsive to the bio-sensor, toemit a second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region; a power sensor to receive the first light from thewave-guide and convert the received first light into electrical energy;and a plurality of switchable capacitors operatively connected to anoutput of the power sensor.

A further aspect of the present invention is a tissue invasive photonicsystem. The tissue invasive photonic system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength and a second light having a second wavelength; a wave-guidebetween the proximal end and distal end of the photonic lead; aradiation scattering medium at the distal end of the photonic lead toreceive radiation from the wave-guide; a plurality of power sensors toreceive scattered radiation from the radiation scattering medium andconvert the received scattered radiation into electrical energy; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; a distal sensor, inthe distal end of the photonic lead, responsive to the bio-sensor, toreflect the second light back to the proximal end of the photonic leadsuch that a characteristic of the second light is modulated to encodethe sensed characteristics of the predetermined tissue region; and abeam splitter to direct the second light to the distal sensor.

A further aspect of the present invention is a tissue invasive photonicsystem. The tissue invasive photonic system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength and a second light having a second wavelength; a firstwave-guide between the proximal end and distal end of the photonic lead;a second wave-guide, having a plurality of power beam splitters thereinat the distal end of the photonic lead to receive and reflect the firstlight from the first wave-guide; a plurality of power sensors to receivethe first light from the power beam splitters in the second wave-guideand convert the received first light into electrical energy; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; a sensor beam splitterto reflect the second light from the first wave-guide; and a distalsensor, in the distal end of the photonic lead, responsive to thebio-sensor, to receive the second light from the sensor beam splitterand to reflect the second light back to the proximal end of the photoniclead such that a characteristic of the second light is modulated toencode the sensed characteristics of the predetermined tissue region.

A further aspect of the present invention is a tissue invasive photonicsystem. The tissue invasive photonic system a photonic lead having aproximal end and a distal end; a light source, in the proximal end ofthe photonic lead, to produce a first light having a first wavelengthand a second light having a second wavelength; a wave-guide between theproximal end and distal end of the photonic lead; a plurality of powersensors to receive the first light from the wave-guide and convert thereceived first light into electrical energy, each power sensor absorbinga fraction of the received first light; a bio-sensor, in the distal endof the photonic lead, to sense characteristics of a predetermined tissueregion; a sensor beam splitter to reflect the second light from thewave-guide; and a distal sensor, in the distal end of the photonic lead,responsive to the bio-sensor, to receive the second light from thesensor beam splitter and to reflect the second light back to theproximal end of the photonic lead such that a characteristic of thesecond light is modulated to encode the sensed characteristics of thepredetermined tissue region.

A further aspect of the present invention is a tissue invasive photonicsystem. The tissue invasive photonic system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength and a second light having a second wavelength; a wave-guidebetween the proximal end and distal end of the photonic lead; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; a sensor beam splitterto reflect the second light from the wave-guide; a distal sensor, in thedistal end of the photonic lead, responsive to the bio-sensor, toreceive the second light from the sensor beam splitter and to reflectthe second light back to the proximal end of the photonic lead such thata characteristic of the second light is modulated to encode the sensedcharacteristics of the predetermined tissue region; a power sensor toreceive the first light from the wave-guide and convert the receivedfirst light into electrical energy; and a plurality of switchablecapacitors operatively connected to an output of the power sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may take form in various components andarrangements of components, and in various steps and arrangements ofsteps. The drawings are only for purposes of illustrating a preferredembodiment and are not to be construed as limiting the presentinvention, wherein:

FIGS. 1 and 2 are illustrations of conventional techniques used toprotect against electromagnetic interference;

FIG. 3 is a block diagram of one embodiment of a MRI immune cardiacassist system according to some or all of the concepts of the presentinvention;

FIG. 4 is a block diagram of another embodiment of a MRI immune cardiacassist system according to some or all of the concepts of the presentinvention;

FIGS. 5 through 20 are schematics of various optical sensing devicesaccording to some or all of the concepts of the present invention;

FIG. 21 illustrates a pressure optical transducer according to some orall of the concepts of the present invention;

FIGS. 22 through 26 are block diagrams of various pressure opticaltransducers according to some or all of the concepts of the presentinvention;

FIG. 27 is a partial view of a cardiac assist device according to someor all of the concepts of the present invention with an intermediateportion of the photonic catheter thereof removed for illustrativeclarity;

FIG. 28 is an enlarged partial perspective view of components located atthe distal end of the photonic catheter FIG. 27;

FIG. 29 is a detailed partial schematic view showing one construction ofan electro-optical transducer according to some or all of the conceptsof the present invention;

FIG. 30 illustrates a block diagram of a cardiac assist system;

FIG. 31 is a graph depicting a typical pulse sequence used in pacing ahuman heart, over an interval equivalent to a nominal 1 Hz humanheartbeat;

FIG. 32 is a similar graph depicting the pacing pulse as shown in FIG.31, but with a much finer time scale;

FIG. 33 is a schematic representation of a cardiac pacing lead with twoelectrodes;

FIG. 34 is a schematic representation of a similar cardiac pacing leadwith three electrodes;

FIG. 35 is a schematic representation of yet another cardiac pacing leadwith two pairs of electrodes;

FIG. 36 is a graph depicting the use of pulsewidth pacing signals andinterleaved periods for sensing heart activity;

FIG. 37 is a graph depicting the operation of one embodiment accordingto some or all of the concepts of the present invention that gainsenergy efficiency by means of early termination of the pacing signal;

FIG. 38 is a graph depicting the operation of another embodimentaccording to some or all of the concepts of the present invention thatgains energy efficiency by means of both early termination of the pacingsignal and by gradient pulsewidth power control;

FIG. 39 is another graph of the embodiment in FIG. 38, but withalternate waveform of the pacing signal;

FIGS. 40 through 42 are schematic circuit diagrams of a pulse generatoraccording to some or all of the concepts of the present invention;

FIG. 43 is a schematic circuit diagram showing one embodiment of anopto-electric coupling device according to some or all of the conceptsof the present invention;

FIGS. 44 and 45 are graphical illustrations of pulse waveforms that maybe, respectively, input to and output from the opto-electric couplingdevice according to some or all of the concepts of the presentinvention;

FIG. 46 is a schematic circuit diagram showing a second embodiment of anopto-electric coupling device in accordance with the invention;

FIG. 47 is a schematic circuit diagram showing a constant currentregulator for a laser light generator according to some or all of theconcepts of the present invention;

FIG. 48 is a detailed partial schematic view showing one construction ofan electro-optical transducer according to some or all of the conceptsof the present invention;

FIG. 49 is a schematic circuit diagram of a pulse generator according tosome or all of the concepts of the present invention;

FIG. 50 is an exploded perspective view of a hermetic component housingaccording to some or all of the concepts of the present invention;

FIGS. 51 through 53 are sectional axial centerline views showingalternative ways in which the component housing of FIG. 50 can beconfigured;

FIG. 54 is a perspective view of the component housing of FIG. 50showing details of exemplary components that may be housed therein;

FIG. 55 is a partial exploded perspective view of a hermetic componenthousing according to some or all of the concepts of the presentinvention;

FIGS. 56 and 57 are sectional axial centerline views showing alternativeways in which the component housing of FIG. 55 can be configured;

FIG. 58 is a perspective view of the component housing of FIG. 55showing details of exemplary components that may be housed therein;

FIG. 59 is a partially exploded perspective view of a hermetic componenthousing according to some or all of the concepts of the presentinvention;

FIG. 60 is a sectional view taken along the axial centerline of thecomponent housing of FIG. 59;

FIG. 61 is a perspective view of the component housing of FIG. 59showing details of exemplary components that may be housed therein; and

FIGS. 62 through 65 are schematics of various optical pressuretransducers according to some or all of the concepts of the presentinvention;

FIGS. 66 through 69 are schematics of various MRI coils for a photoniccatheter according to some or all of the concepts of the presentinvention; and

FIGS. 70 through 85 are schematics of various optical power transferdevices according to some or all of the concepts of the presentinvention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

As noted above, the present invention is directed to an implantabledevice that is immune or hardened to electromagnetic insult orinterference.

FIG. 3 illustrates a cardiac assist system that is immune or hardenedelectromagnetic insult or interference, namely to magnetic radiationimaging, MRI. As illustrated in FIG. 3, a main module 40 includes aprocessor circuit 43 that controls the operations of the cardiac assistsystem. The processor unit 43 provides control signals to a pacing unit45. The pacing unit 45 produces packets of energy to stimulate the heart49 to start beating or to beat at a predetermined rate or pace. Theprocessor circuit 43 also receives information about the conditions ofthe heart 49 from a sensing unit 44. The sensing unit 44, throughsensors or electrodes, monitors the conditions of the heart 49 toprovide feedback information to the processor circuit 43.

A telemetry unit 46 is also provided in the main module 40 to provideinformation to the processor circuit 43 received from sources externalto the body. Lastly, a timing circuit 42 is provided to communicate withan auxiliary module 50 through an optical communication interface 41 inthe main module 40, over optical communication channels 36, such asfiber optics, and through an optical communication interface 46 in theauxiliary module 50. In response to the information received from theoptical communication interface 46, a signaling logic circuit 47 willactivate or suppress a pacing unit 48. In this embodiment, if there is afailure in the main module 40 due to error or electromagnetic insult orinterference, the signaling logic circuit 47 will detect the shutdown ofthe main module 40 and cause the auxiliary module 50 to take over thepacing of the heart 49 in an asynchronous manner through pacing unit 48.

As described above, the cardiac assist system performs synchronouscardiac assist operations through a main module. A secondary module isprovided to perform asynchronous cardiac assist operations. Upondetection of an electromagnetic interference insult upon the cardiacassist system, the control circuit of the main module terminatessynchronous cardiac assist operations, and the control circuit of thesecondary module initiates asynchronous cardiac assist operations upondetection of the electromagnetic interference insult. The controlcircuit of the secondary module places the cardiac assist system in theasynchronous mode for a duration of the electromagnetic interferenceinsult and terminates the asynchronous mode of the cardiac assist systemupon detection of an absence of an electromagnetic interference insult.The control circuit of the main module terminates the synchronous modeof the cardiac assist system for the duration of the electromagneticinterference insult and re-initiates the synchronous mode of the cardiacassist system upon detection of an absence of an electromagneticinterference insult.

FIG. 4 is a more detail schematic of FIG. 3. In FIG. 4, a cardiac assistsystem is immune or hardened electromagnetic insult or interference,namely to magnetic radiation imaging, MRI. As illustrated in FIG. 4, amain module 67 includes a parallel processing unit 59 and primary andsecondary processors 65 and 63 that control the operations of thecardiac assist system. The parallel processing unit 59 provides controlsignals to a pacing unit 58. The pacing unit 58 produces packets ofenergy to stimulate the heart to start beating or to beat at apredetermined rate or pace through lead(s) 51 and electrode 52. Theparallel processing unit 59 also receives information about theconditions of the heart 49 from a sensor 53 through lead(s) 56. Thesensor 53 monitors the conditions of the heart to provide feedbackinformation to the parallel processing unit 59.

A telemetry unit 62 is also provided in the main module 67 to provideinformation to the parallel processing unit 59 received from sources 60external to the body. Memory 72 is provided for the processing of thecardiac assist system, and a primary error detection circuit 64 isincluded to detect any failures in the main module 67. Lastly, a timingcircuit 66 is provided to communicate with an auxiliary module 69through an optical emitter 68 in the main module 67, over opticalcommunication channels 70, such as fiber optics, and through a lightdetection and signaling circuit 73 in the auxiliary module 69.

In response to the information received from the light detection andsignaling circuit 73, a pacing unit 74 will activate or de-activate. Inthis embodiment, if there is a failure in the main module 67 due toerror or electromagnetic insult or interference, the light detection andsignaling circuit 73 will detect the shutdown of the main module 67 andcause the auxiliary module 69 to take over the pacing of the heart in anasynchronous manner through pacing unit 74, lead(s) 55, and electrode54.

As described above, the cardiac assist system performs synchronouscardiac assist operations through a main module. A secondary module isprovided to perform asynchronous cardiac assist operations. Upondetection of an electromagnetic interference insult upon the cardiacassist system, the control circuit of the main module terminatessynchronous cardiac assist operations, and the control circuit of thesecondary module initiates asynchronous cardiac assist operations upondetection of the electromagnetic interference insult. The controlcircuit of the secondary module places the cardiac assist system in theasynchronous mode for a duration of the electromagnetic interferenceinsult and terminates the asynchronous mode of the cardiac assist systemupon detection of an absence of an electromagnetic interference insult.The control circuit of the main module terminates the synchronous modeof the cardiac assist system for the duration of the electromagneticinterference insult and re-initiates the synchronous mode of the cardiacassist system upon detection of an absence of an electromagneticinterference insult.

FIG. 30 illustrates a cardiac assist system that includes a primarydevice housing 1100. The primary device housing 1100 includes a controlcircuit 1110, such as a microprocessor integrated circuit forcontrolling the operations of the cardiac assist system. The controlcircuit 1110 may select a mode of operation for the cardiac assistsystem based on predetermined sensed parameters. The primary devicehousing 1100 may also include circuitry (not shown) to detect andisolate cross talk between device pulsing operations and device sensingoperations. The control circuit 1110 may isolate physiological signalsusing a noise filtering circuit or a digital noise filtering.

The primary device housing 1100 is implantable such that the controlcircuit 1110 can be programmable from a source external of the primarydevice housing 1100 or the control circuit 1110 can providephysiological diagnostics to a source external of the primary devicehousing 1100.

The primary device housing 1100 includes a power source 1120. The powersource 1120 may be a battery power source in combination with a batterypower source measuring circuit. In this embodiment, the control circuit1110 can automatically adjust a value for determining an electivereplacement indication condition of a battery power source such that thevalue is automatically adjusted by the control circuit 1110 in responseto a measured level of a state of the battery power source, the measuredlevel generated by the battery power source measuring circuit connectedto the battery power source.

The primary device housing 1100 includes an optical emitter 1130, anoptical sensor 1140, and an interface 1170 to put the primary devicehousing 1100 in operative communication with a lead system 1150.

The primary device housing 1100 may also include a switch (not shown),such as a reed switch or solid state switch, to place the controlcircuit 1110 into a fixed-rate mode of operation and an acoustic sensor(not shown) or near infrared sensor (not shown) to sense a predeterminedacoustic signal. The switch places the control circuit 1110 into afixed-rate mode of operation when the acoustic sensor or near infraredsensor senses the predetermined acoustic signal or the predeterminedinfrared signal.

The primary device housing 1100 has formed around it a shield 1160 toshield the primary device housing 1100 and any circuits therein fromelectromagnetic interference.

The shield 1160 may be a metallic sheath, a carbon composite sheath, ora polymer composite sheath to shield the primary device housing 1100 andany circuits therein from electromagnetic interference. The shield 1160is further covered with a biocompatible material wherein thebiocompatible material may be a non-permeable diffusion resistantbiocompatible material. The primary device housing 1100 may also includea detection circuit (not shown) to detect a phase timing of an externalelectromagnetic field such that the control circuit 1110 alters itsoperations to avoid interfering with the detected externalelectromagnetic field.

FIG. 30 further illustrates a lead system 1150 connected to the primarydevice housing 1100. The lead system 1150 provides a communication pathfor information to be transported between the primary device housing1100 and a distal location in the body. The lead system 1150 also may bea conduit of power or energy from the primary device housing 1100 to thedistal location in the body.

In the example illustrated in FIG. 30, the lead system 1150 may providea path for control signals to be transferred to the distal location ofthe body, such as the heart muscle tissue. These control signals areused to control the operations of a secondary device 1200, such asstimulating the beating of the heart. The lead system 1150 may alsoprovide a path for signals representing sensed biological conditions tobe transferred from the distal location of the body to the primarydevice housing 1100 so that the functionality of the heart muscle tissuecan be effectively monitored.

The lead system 1150 may be a fiber optic based communication systemwherein the fiber optic communication system contains at least onechannel within a multi-fiber optic bundle. The fiber optic basedcommunication system is covered with a biocompatible material whereinthe biocompatible material is a non-permeable diffusion resistantbiocompatible material.

The lead system 1150 may also be a plurality of electrical leads thathave a shield 1180 therearound to prevent the electrical leads fromconducting stray electromagnetic interference. This shield 1180 may be ametallic sheath, a carbon composite sheath, or a polymer compositesheath to prevent the electrical leads from conducting strayelectromagnetic interference. In addition to the shield 1180 or in lieuof the shield 1180, each electrical lead may include an electricalfilter wherein the electrical filter removes stray electromagneticinterference from a signal being received from the electrical lead. Theelectrical filter may comprise capacitive and inductive filter elementsadapted to filter out predetermined frequencies of electromagneticinterference. The shield 1180 is covered with a biocompatible materialwherein the biocompatible material is a non-permeable diffusionresistant biocompatible material.

The electrical leads maybe unipolar leads, bipolar leads, or acombination of unipolar and bipolar leads. The lead system 1150 may alsobe a combination of a fiber optic based communication system andelectrical leads.

The lead system 1150 may also include a detection circuit (not shown) todetect a phase timing of an external electromagnetic field such that thecontrol circuit 1110 alters its operations to avoid interfering with thedetected external electromagnetic field.

In FIG. 30, the secondary housing 1200 includes a control circuit 1210,such as a microprocessor integrated circuit. The secondary devicehousing 1200 may also include circuitry (not shown) to detect andisolate cross talk between device pulsing operations and device sensingoperations. The control circuit 1210 may isolate physiological signalsusing a noise filtering circuit or a digital noise filtering.

The secondary device housing 1200 includes a power source 1220. Thepower source 1220 may be a battery power source or capacitor or otherdevice for storing. The primary device housing 1200 includes an opticalemitter 1230, an optical sensor 1240, and an interface 1270 to put thesecondary device housing 1200 in operative communication with the leadsystem 1150.

The secondary device housing 1200 has formed around it a shield 1260 toshield the secondary device housing 1200 and any circuits therein fromelectromagnetic interference.

The shield 1260 may be a metallic sheath, a carbon composite sheath, ora polymer composite sheath to shield the secondary device housing 1200and any circuits therein from electromagnetic interference. The shield1260 is further covered with a biocompatible material wherein thebiocompatible material may be a non-permeable diffusion resistantbiocompatible material.

The secondary housing 1200 may also include electrodes 1300 for eitherstimulating a tissue region or sensing biological characteristics orparameters from the tissue region. More details as to the constructionof the secondary device are set forth below in the describing of distalend elements.

As an alternative to electrodes 1300, the secondary device housing 1200may include a sensing and stimulation system that includes opticalpulsing components to deliver a stimulus of a predetermined duration andpower to the desired anatomical cardiac tissue region; a sensing andstimulation system that includes optical pulsing components to deliver astimulus of a predetermined duration and power to the desired anatomicalcardiac tissue region and electrical pulsing components to deliver astimulus of a predetermined duration and power to the desired anatomicalcardiac tissue region; a hydrostatic pressure sensing components todetect physiological signals from the desired anatomical cardiac tissueregion; or optical sensing components to detect physiological signalsfrom the desired anatomical cardiac tissue region and electrical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

The secondary device housing 1200 may also include a detection circuit(not shown) to detect a phase timing of an external electromagneticfield such that the control circuit 1110 alters its operations to avoidinterfering with the detected external electromagnetic field.

The secondary device housing 1200 may include sensors to detect a heartsignal and to produce a sensor signal therefrom and a modulator tomodulate the sensor signal to differentiate the sensor signal fromelectromagnetic interference. In the alternative, the secondary devicehousing 1200 may include sensors to detect a heart signal and to producea sensor signal therefrom, and the primary device housing 1100 mayinclude a sampling circuit to sample the sensor signal multiple times todifferentiate the sensor signal from electromagnetic interference,undesirable acoustic signals, large muscle contractions, or extraneousinfrared light.

The cardiac assist system illustrated in FIG. 30 may detect anelectromagnetic interference insult upon the cardiac assist system, andupon detection, the control circuit 1110 places the cardiac assistsystem in an asynchronous mode. The control circuit 1110 places thecardiac assist system in the asynchronous mode for a duration of theelectromagnetic interference insult and places the cardiac assist systemin a synchronous mode upon detection of an absence of an electromagneticinterference insult. The electromagnetic interference insult may bedetected a thermistor or other heat detector, a high frequencyinterference detector, a high voltage detector, or an excess currentdetector.

The cardiac assist system illustrated in FIG. 30 may also provide atrialmonitoring and diagnostic functions to help physicians make more precisepatient management decisions. The cardiac assist system illustrated inFIG. 30 can provide bradyarrhythmia therapies that treat patients withchronic heart problems in which the heart beats too slowly to adequatelysupport the body's circulatory needs, in addition to the monitoring ofthe atria (upper chambers) and ventricles (lower chambers) to enablephysicians to assess atrial rhythm control and ventricular rate control.

The cardiac assist system illustrated in FIG. 30 can also be used toprovide daily atrial fibrillation measurements to assess atrial rhythmcontrol. This information can improve a physician's ability to trackdisease progression, as well as the effectiveness of current device anddrug therapies. The cardiac assist system illustrated in FIG. 30 canalso be used to monitor of the ventricular rate during an atrialarrhythmia that helps assess ventricular rate control. This informationcan be viewed in a graphical snapshot format or by viewing the specificepisode EGM information. The cardiac assist system illustrated in FIG.30 can also be used to provide specific information on the frequency andduration of arrhythmias that help with risk assessment of symptoms andin determining whether a change in anticoagulation medicines iswarranted.

FIG. 27 illustrates an MRI-compatible cardiac pacemaker according toanother embodiment of the present invention. The pacemaker may bewearable and is readily implemented to operate in a fixed-rate (VOO)mode. The pacemaker includes a first (main) enclosure 263 that isdesigned to be located outside the body and connected to a proximal end268 of a photonic catheter. A distal end 273 of a photonic catheter 271mounts a bipolar endocardial (or pericardial) electrode pair 286 thatincludes a second enclosure 283 and a third enclosure 285 separated by ashort insulative spacer 284. Other electrode configurations could alsobe used.

The main enclosure 263 houses a self-contained electrical power source264, a pulse generator 265, and an electro-optical transducer 266. Thepower source 264, which may include one or more batteries, serves todeliver low energy continuous electrical power to the pulse generator.The pulse generator 265 stores the electrical energy provided by thepower source 264 in one or more storage devices such as capacitors,batteries, etc., and periodically releases that energy to deliverelectrical pulses to the electro-optical transducer 266. Theelectro-optical transducer 266 converts the electrical pulses into lightenergy and directs that energy into the proximal end 268 of the photoniccatheter 271.

The main enclosure 263 is preferably formed as a sealed casing, externalto the body, made from a non-magnetic metal. Note that a rate controlselector and a pulse duration selector can be provided on the mainenclosure 263 to allow a medical practitioner to controllably stress apatient's heart by varying the rate and duration of the stimulatingpulses. Note further that if the power source 264 comprises multiplebatteries, these may be separately wired for independent operation and aselector switch can be provided on the enclosure 263 to selectivelyactivate each battery for use. A pair of illuminated push buttons mayalso be provided for testing each battery.

The photonic catheter 271 includes an optical conduction pathway 267surrounded by a protective outer covering 269. The optical conductionpathway 267 may be constructed with one or more fiber optic transmissionelements that are conventionally made from glass or plastic fibermaterial, e.g., a fiber optic bundle. To avoid body fluidincompatibility problems, the protective outer covering 269 should bemade from a biocompatible material, such as silicone rubber,polyurethane, polyethylene, or other biocompatible polymer having therequired mechanical and physiological properties. The protective outercovering 269 is thus a biocompatible covering. Insofar as the photoniccatheter 271 must be adapted for insertion into the body, thebiocompatible covering 269 is preferably a very thin-walled elongatedsleeve or jacket having an outside diameter on the order of about 5millimeters and preferably as small as one millimeter or even smaller.This will render the photonic catheter 271 sufficiently slender tofacilitate insertion thereof through a large vein, such as the externaljugular vein.

The proximal end 268 of the photonic catheter 271 is mounted to the mainenclosure 263 using an appropriate connection. The optical conductionpathway 267 may extend into the enclosure 263 for a short distance,where it terminates in adjacent relationship with the electro-opticaltransducer 266 in order to receive light energy therefrom.

Light emitted by the electro-optical transducer 266 is directed into theproximal end 268 of the photonic catheter 271, and transmitted throughthe optical conduction pathway 267 to the second enclosure 283. Sincethe photonic catheter 271 is designed for optical transmission, itcannot develop magnetically induced or RF-induced electrical currents,as is the case with the metallic leads of conventional pacemakercatheters.

The second enclosure 283 houses an opto-electrical transducer 274, whichconverts light energy received from the distal end of the photoniccatheter 271 into electrical energy. The electrical output side 280 ofthe opto-electrical transducer 274 delivers electrical pulses that drivethe pacemaker's electrode pair 286.

The second enclosure 283 is a hermetically sealed casing made from anon-magnetic metal, such as titanium, a titanium-containing alloy,platinum, a platinum-containing alloy, or any other suitable metal,including copper plated with a protective and compatible coating of theforegoing materials. Plated copper is especially suitable for the secondenclosure 283 because it has a magnetic susceptibility approaching thatof the human body, and will therefore minimize MRI image degradation.Note that the magnetic susceptibility of human body tissue is very low,and is sometimes diamagnetic and sometimes paramagnetic. As analternative to using non-magnetic metals, the second enclosure 283 canbe formed from an electrically conductive non-metal that preferably alsohas a very low magnetic susceptibility akin to that of the human body.Non-metals that best approach this condition include conductivecomposite carbon and conductive polymers comprising silicone,polyethylene, or polyurethane.

Unlike the main enclosure 263, the second enclosure 283 is adapted to beimplanted via insertion in close proximity to the heart, and inelectrical contact therewith. As such, the second enclosure 283preferably has a miniaturized tubular profile that is substantiallyco-equal in diameter with the photonic catheter 271.

As seen In FIGS. 27 and 28, the second enclosure (283, 295) includes acylindrical outer wall 276 and a pair of disk-shaped end walls 272 and277. The end wall 272 is mounted to the distal end 273 of the photoniccatheter 271 using an appropriate sealed connection that preventspatient body fluids from contacting the optical conduction pathway 267and from entering the second enclosure (283, 295). Although the photoniccatheter 271 may feed directly from the main enclosure 263 to the secondenclosure (283, 295), another arrangement would be to provide an opticalcoupling 270 at an intermediate location on the photonic catheter 271.The coupling 270 could be located so that a distal portion of thephotonic catheter 271 that connects to the second enclosure 283protrudes a few inches outside the patient's body. A proximal portion ofthe photonic catheter 271 that connects to the main enclosure 263 wouldthen be connected when MRI scanning is to be performed. Note that themain enclosure 263 could thus be located a considerable distance fromthe patient so as to be well outside the area of the MRI equipment, asopposed to being mounted on the patient or the patient's clothing.

In an alternative arrangement, the coupling 270 could be located at themain enclosure 263. The optical conduction pathway 267 may extend intothe enclosure (283, 295) for a short distance, where it terminates inadjacent relationship with the opto-electrical transducer (274, 289) inorder to deliver light energy thereto. Light received by theopto-electrical transducer (274, 289) will thus be converted toelectrical energy and delivered to the output side 280 of theopto-electrical transducer (274, 289).

Due to the miniature size of the second enclosure (283, 295), theopto-electrical transducer (274, 289) needs to be implemented as aminiaturized circuit. However, such components are conventionallyavailable from commercial electronic component manufacturers. Note thatthe opto-electrical transducer (274, 289) also needs to be adequatelysupported within the second enclosure (283, 295).

To that end, the second enclosure (283, 295) can be filled with asupport matrix material 291 that may be the same material used to formthe photonic catheter's biocompatible covering 269 (e.g., siliconerubber, polyurethane, polyethylene, or any biocompatible polymer withthe required mechanical and physiological properties).

As stated above, the second enclosure (283, 295) represents part of anelectrode pair (286, 298) that delivers the electrical output of thepacemaker to a patient's heart. In particular, the electrode pair (286,298) is a tip/ring system and the second enclosure (283, 295) is used asan endocardial (or pericardial) ring electrode thereof. A positiveoutput lead (275, 290) extending from the electrical output side 280 ofthe opto-electrical transducer (274, 289) is electrically connected tothe cylindrical wall 276 of the second enclosure (283, 295), as bysoldering, welding or the like. A negative output lead (281, 294)extending from the electrical output side 280 of the opto-electricaltransducer (274, 289) is fed out of the second enclosure (283, 295) andconnected to a third enclosure (285, 297), which functions as anendocardial tip electrode of the electrode pair (286, 298).

The third enclosure (285, 297) can be constructed from the samenon-magnetic metallic material, or non-metal material, used to form thesecond enclosure (283, 295). Since it is adapted to be inserted in apatient's heart as an endocardial tip electrode, the third enclosure(285, 297) has a generally bullet shaped tip (279, 293) extending from atubular base end (278, 292). The base end (278, 292) preferably has anoutside diameter that substantially matches the diameter of the secondenclosure (283, 295) and the photonic catheter 271. Note that the baseend (278, 292) of the third enclosure (285, 297) is open insofar as thethird enclosure (285, 297) does not house any critical electricalcomponents. Indeed, it mounts only the negative lead (281, 294) that iselectrically connected to the third enclosure's base end (278, 292), asby soldering, welding, or the like.

The material used to form the spacer (284, 296) preferably fills theinterior of the second enclosure (283, 295) so that there are no voidsand so that the negative lead (281, 294) is fully captured therein.

In FIG. 29, electrical power source 303 is implemented using a pair ofconventional pacemaker lithium batteries 300 providing a steady state DCoutput of about 3 to 9 volts. Electro-optical transducer 301 isimplemented with light emitting or laser diodes 304 and current limitingresistors 305. The diodes 304 are conventional in nature and thus have aforward voltage drop of about 2 volts and a maximum allowable currentrating of about 50-100 milliamperes, or more. If additional supplyvoltage is available from the power source 20 (e.g., 4 volts or higher),more than one diode can be used in the electro-optical transducer foradditional light energy output. The value of each resistor 305 isselected accordingly.

By way of example, if the batteries 300 produce 3 volts and the desiredcurrent through a single diode is 0.5 milliamperes, the value of theresistor should be about 2000 ohms. This would be suitable if the diodeis a light emitting diode. If the diode were a laser diode, other valuesand components would be used. For example, a current level on the orderof 100 milliamps may be required to produce coherent light output fromthe diode if it is a laser. The optical conduction pathway 300 can beimplemented as fiber optic bundles 307, or as single fibers, drivingrespective arrays of photo diodes. The opto-electrical transducer 28 maybe implemented with six photodiodes 312-317 that are wired forphotovoltaic operation.

The opto-electrical transducer 309 may be implemented with a singlephotodiode that is wired for photovoltaic operation. The photodiodes aresuitably arranged so that each respectively receives the light output ofone or more fibers of the fiber optic bundles and is forward biased intoelectrical conduction thereby.

Each photodiode is conventional in nature and thus produces a voltagedrop of about 0.6 volts. Cumulatively, the photodiodes develop a voltagedrop of about 3.3 volts across the respective positive and negativeinputs a power amplifier (not shown). The photodiode develops about 0.6volts across the respective positive and negative inputs of the poweramplifier.

FIGS. 40-42 and 49 shows an alternative circuit configuration that maybe used to implement the oscillator (369, 372, 373, 439) and the poweramplifier. The alternative circuit configurations are conventional innature and do not constitute part of the present invention per se. Thealternative circuit configurations are presented herein as examples ofpulsing circuits that have been shown to function well in a pacemakerenvironment. In FIGS. 40-42, the oscillator (369, 372, 373, 439) is asemiconductor pulsing circuit (365, 370, 374, 441) of the type disclosedin U.S. Pat. No. 3,508,167. As described in U.S. Pat. No. 3,508,167, thecontents of which are incorporated herein by reference, the pulsingcircuit (365, 370, 374, 441) forming the oscillator (369, 372, 373, 439)provides a pulsewidth and pulse period that are relatively independentof load and supply voltage. The semiconductor elements are relegated toswitching functions so that timing is substantially independent oftransistor gain characteristics. In particular, a shunt circuitincluding a pair of diodes is connected so that timing capacitor chargeand discharge currents flow through circuits that do not include thebase-emitter junction of a timing transistor.

In FIG. 46, an opto-electrical coupling device 399 is shown. Theopto-electrical coupling device includes opto-electrical transducer 392.A high quality capacitor 390 delivers pulses from the opto-electricaltransducers photodiode array (393-398) to a tip electrode 401. A returnpath is provided from a ring electrode 400. The capacitor 390 forms partof a DC current discharge system 391 that also includes a resistor 389.The resistor 389 is connected across the capacitor 390 to discharge itbetween pulses. Exemplary values for the capacitor 390 and the resistor389 are 10 microfarads and 20 K ohms, respectively.

In FIG. 47, a constant current regulator 402 is shown. The purpose ofthe constant current regulator 402 is to controllably drive theelectro-optical transducer 405 using the electrical pulse output of apulse generator. Collectively, the constant current regulator 402 andthe electro-optical transducer 405 provide a constant current regulatedlaser light generator 404. The current regulator 402 uses an NPNtransistor 403 arranged in a common emitter configuration to drive thelaser diode 404. A suitable NPN transistor that may be used to implementthe transistor 403 is a switching transistor.

The laser diode 404 can be implemented as a standard 150 milliwattgallium arsenide laser diode. The recommended power level for drivingsuch a device is about 100 milliwatts. The required input voltage isabout 2 volts. Assuming there is a conventional diode voltage drop ofabout 0.7 volts across the laser diode 404, a driving current of about140 milliamps should be sufficient to achieve operation at the desired100 milliwatt level. However, the current through the laser diode 404must be relatively constant to maintain the desired power output. Theconstant current regulator 402 achieves this goal.

In particular, the base side of the transistor 403 is biased through aresister RI and a pair of diodes D1 and D2. The diodes D1 and D2 areconnected between the base of the transistor 403 and ground. Each has aconventional diode voltage drop of about 0.7 volts, such that the totalvoltage drop across the diodes D1 and D2 is about 1.5 volts and issubstantially independent of the current through the diodes (atoperational current levels). This means that the base of the transistor403 will be maintained at a relatively constant level of about 1.5 voltsnotwithstanding changes in the input voltage supplied from the pulsegenerator. The value of the resistor R1 is selected to be relativelyhigh to reduce the current draw through the base of the transistor 403.By way of example, a value of 2500 ohms may be used for R1. Assuming asupply voltage of about 5 volts, as represented by the input pulsewaveform, the current through the resistor R1 will be a negligible 1.4milliamps.

Importantly, the emitter side of the transistor 403 will remain at arelatively constant level of about 1 volt (assuming a base-emittervoltage drop across the transistor 403 of about 0.5 volts). A resistorR2 is placed between the emitter of the transistor 403 and ground inorder to establish a desired current level through the collector-emittercircuit of the transistor 403. Note that this also represents thedriving current through the laser diode 404 insofar as the laser diodeis connected in series between the current regulator's supply voltage(the output of pulse generator) and the collector of the transistor 406.Since the voltage potential at the transistor emitter is about 1 volt,if R2 is selected to be a 7 ohm resistor, the resultant current levelwill be about 140 milliamps. This corresponds to the current levelrequired to drive the laser diode 404 at the desired operational powerlevel.

In FIG. 48, an electrical power source (409, 411) is implemented using apair of conventional pacemaker lithium batteries (408, 410) providing asteady state DC output of about 3 to 9 volts. The electro-opticaltransducers 412 and 416 are implemented with light emitting or laserdiodes (414, 415) and current limiting resistors (413, 419). The diodesare conventional in nature and thus have a forward voltage drop of about2 volts and a maximum allowable current rating of about 50-100milliamps, or more. If additional supply voltage is available from thepower source (409, 411) (e.g., 4 volts or higher), more than one diodecan be used in each electro-optical transducer 412 and 416 foradditional light energy output. The value of each resistor is selectedaccordingly.

By way of example, if the batteries produce 3 volts and the desiredcurrent through a single diode is 0.5 milliamps, the value of theresistor should be about 2000 ohms. This would be suitable if the diodeis a light emitting diode. If the diode were a laser diode, other valuesand components would be used. For example, a current level on the orderof 100 milliamps may be required to produce coherent light output fromthe diode if it is a laser. The optical conduction pathways 417 and 421can be implemented as fiber optic bundles 418 and 423, or as singlefibers, driving respective arrays of photodiodes.

The opto-electrical transducer 424 may be implemented with sixphotodiodes 428-433 that are wired for photovoltaic operation. Theopto-electrical transducer 424 may be implemented with a singlephotodiode 434 that is wired for photovoltaic operation. The photodiodesare suitably arranged so that each respectively receives the lightoutput of one or more fibers of the fiber optic bundles 418 and 423 andis forward biased into electrical conduction thereby.

Each photodiode is conventional in nature and thus produces a voltagedrop of about 0.6 volts. Cumulatively, the photodiodes 428-433 develop avoltage drop of about 3.3 volts across the respective positive andnegative inputs 426 and 435 of the power amplifier 427. The photodiode434 develops about 0.6 volts across the respective positive and negativeinputs 437 and 438 of the power amplifier 427.

In FIG. 43, a circuit diagram of an opto-electric coupling device 388 isshown. The opto-electric coupling device 388 includes theopto-electrical transducer 376, which is assumed to be illuminated by aphotonic catheter for about 1 millisecond, and left dark for about 1000milliseconds. When illuminated, opto-electrical transducer photodiodearray 377-382 will produce pulses of about 3 to 4 volts across itsoutputs. The positive side of the photodiode array is connected via ahigh quality capacitor 385 to an implantable tip electrode 383 that isadapted to be implanted in the endocardium of a patient. The negativeside of the photodiode array is connected to an implantable ringelectrode 384 that is adapted to be immersed in the blood of thepatient's right ventricle. A DC current discharge system 387 comprisingthe capacitor 385 and a resistor 386 is used to attenuate DC current inthe tissue implanted with the electrodes 383 and 384.

The resistor 386 is connected across the outputs of the photodiodearray. The resistor 386 thus grounds one side of the capacitor 385between pulses. The return path from the implanted tissue is the throughthe ring electrode 384.

The values of the capacitor and the resistor are selected so that theopto-electric coupling device conveys a suitable stimulating signal tothe electrodes, but in such a manner as to prevent any net DC currentfrom flowing into the implanted tissue. A long RC time constant isdesired so that the square waveform of the photodiode array output isdelivered in substantially the same form to the implanted tissue. For a1 millisecond pulse, the desired RC time constant should besubstantially larger than 1 millisecond. By way of example, if thecapacitor has a capacitance of 10 microfarads and the resistor has aresistance of 20K ohms, the RC time constant will be 200 milliseconds.This is substantially larger than the 1 millisecond pulse lengthproduced by the photodiode array.

On the other hand, the RC time constant should not be so large as toprevent adequate DC current flow from the implanted body tissue into thecapacitor between pulses. According to design convention for RCcircuits, a period of five time constants is required in order for an RCcircuit capacitor to become fully charged. Note that the selected RCtime constant of 200 milliseconds satisfies this requirement if thephotodiode array is pulsed at 1000 millisecond intervals, which istypical for pacemakers. Thus, there will be approximately five 200millisecond time constants between every pulse. Stated another way, theRC time constant will be approximately one-fifth of the time intervalbetween successive pulses.

FIG. 44 shows the square wave electrical pulses generated by thephotodiode array. FIG. 45 shows the actual electrical pulses deliveredat the electrodes due to the presence of the RC circuit provided by thecapacitor and the resistor. Note that the pulses of FIG. 45 aresubstantially square is shape due to the RC circuit's time constantbeing substantially larger than the input pulse width. FIG. 45 furthershows that there is a small reverse potential between pulses thatcounteracts DC current build up in the stimulated tissue.

Ideally, the area A₁ underneath each positive pulse of FIG. 45 will beequal to the area A₂ of negative potential that follows the positivepulse.

Another embodiment of the present invention is the use of a photoniccatheter in a MRI environment to sense the biological conditions ofparticular tissue regions of a patient or to stimulate particular tissueregions of the patient. Examples of photonic catheters are illustratedin FIGS. 5 through 20.

In FIGS. 5 and 6, power supply 595 and logic and control unit 597 enableemitter 598 to transmit radiation, preferably optical radiation atwavelength λ₁ through beam splitter 900 into wave-guide 601. Thisradiation exits the wave-guide 601 and passes through beam splitter 606to sensor 607 that converts the radiation to electrical energy. Theelectrical energy is used to directly power functions at the distal endof lead 602, such as stimulation of internal body tissues and organs(e.g. pacing of cardiac tissues) through electrodes 604 and 603. Theelectrical energy is also used to power logic and control unit 608 or isstored in energy storage device 609 (e.g. a capacitor) for later use.Proximally located elements are electrically connected throughconductors. Distally located sensor 607, logic and control unit 608,energy storage device 609, and electrodes (604, 603) are electricallyconnected through conductive elements.

A second emitter 600 transmits radiation at wavelength λ₂ (λ₂≠λ₁)through beam splitter 901, off beam splitter 900, into wave-guide 601,to beam splitter 606 and optical attenuator 605 that is mounted on amirror. The optical attenuator 605 is preferably made from materialssuch as liquid crystals whose optical transmission density is modulatedby applied electrical voltage. The distally located logic and controlunit 608 and optical attenuator 605 are powered either directly byexcitation radiation or from energy stored in energy storage element609.

This photonic catheter can also be used with electrodes 603 and 604 tocapture electrical signals from the patient and direct the capturedelectrical signals to logical and control unit 608 which uses electricalenergy to modulate the optical transmission density of opticalattenuator 605. Attenuated optical signals, originally emanating fromemitter 600, are encoded with the electrical signals received byelectrodes 603 and 604 by passing through the optical attenuator 605,reflect off mirror, travel back through the optical attenuator 605,reflect off beam splitter 606 and into wave-guide 601 to beam splitters900 and 901 to sensor 599 that converts the encoded optical signal to anencoded electrical signal. Output from sensor 599 is sent to logic andcontrol unit 597. This output is either utilized by logic and controlunit 597 to control the radiation from emitter 598, which is typicallyat a high energy level and is used to stimulate distally located tissuesand organs, or is relayed to transmitter 596 which relays this sensoryinformation to external sources.

The embodiment illustrated in FIG. 7 is similar to the embodimentillustrated in FIGS. 5 and 6, with the exception that the opticalattenuator 612 is mounted over the surface of the distally locatedsensor 613 to take advantage of the first surface reflectance of thissensor. Radiation emitted by wave-guide 610 passes through opticalattenuator 612 to sensor 613 that converts the radiation to electricalenergy as previously described. Radiation emitted by wave-guide 610passes through optical attenuator 612 and reflects off the front surfaceof sensor 613. This reflected energy is collected by coupling lens 611that directs the energy into wave-guide 610 to a sensor at the proximalend (not shown).

The embodiment illustrated in FIG. 8 is similar to the embodimentillustrated in FIGS. 5 and 6, with the exception that a variablereflectance optical reflector 616 is mounted over the surface of thedistally located sensor 617. Radiation emitted by wave-guide 619 passesthrough optical reflector 616 to sensor 617 that converts the radiationto electrical energy as previously described. Radiation emitted bywave-guide 619 is reflected off optical reflector 616 and is collectedby coupling lens 618 that directs the energy into wave-guide 619.Preferably, the variable reflectance optical reflector 616 would betransparent to excitation radiation.

With respect to FIGS. 9 and 10, power supply 620 and logic and controlunit 622 enable emitter 623 to transmit radiation, preferably opticalradiation at wavelength λ₁ through beam splitter 624 into wave-guide626. This radiation exits the wave-guide and passes through an on-axisvariable intensity optical emitter 631 to sensor 632 that converts theradiation to electrical energy. The electrical energy is used todirectly power functions at the distal end of lead 635, such asstimulation of internal body tissues and organs (e.g. pacing of cardiactissues) through electrodes 627 and 628; to power logic and control unit633; or to store in energy storage device 634 (e.g. a capacitor) forlater use. Proximally located elements are electrically connectedthrough conductors. Distally located sensor, logic and control unit,energy storage device, and electrodes are electrically connected throughconductive elements.

Logic and control unit 633 receives sensor input from electrodes 627 and628 and delivers an electrical potential to variable intensity opticalemitter 631 causing it to emit optical radiation at wavelength λ₂(λ₂≠λ₁) which is collected by coupling lens 630 and directed intowave-guide 629, to beam splitter 624 and sensor 625. The distallylocated logic and control unit 633 and optical attenuator 631 arepowered either directly by excitation radiation or from energy stored inenergy storage element 634.

This photonic catheter can also be used with electrodes 627 and 628 tocapture electrical signals from the patient and direct the capturedelectrical signals to logical and control unit 633 that uses electricalenergy to modulate the variable intensity optical emitter 631. Opticalsignals, emanating from variable intensity optical emitter 631, areencoded with the electrical signals received by electrodes 627 and 628and travel into wave-guide 629 to beam splitter 624 to sensor 625 thatconverts the encoded optical signal to an encoded electrical signal.Output from sensor 625 is sent to logic and control unit 622. Thisoutput is either utilized by logic and control unit 622 to control theradiation from emitter 623, which is typically at a high energy leveland is used to stimulate distally located tissues and organs, or isrelayed to transmitter 621 which relays this sensory information toexternal sources.

The embodiment illustrated in FIGS. 11 and 12 is similar to theembodiment illustrated in FIGS. 9 and 10, with the exception that thevariable intensity optical emitter 646 is located off-axis. Power supply636 and logic and control unit 638 enable emitter 639 to transmitradiation, preferably optical radiation at wavelength λ₁ through beamsplitter 910 into wave-guide 641. This radiation exits the wave-guide643 and passes through beam splitter 645 to sensor 647 that converts theradiation to electrical energy. The electrical energy is used todirectly power functions at the distal end of lead 642, such asstimulation of internal body tissues and organs (e.g. pacing of cardiactissues) through electrodes 650 and 644; power logic and control unit648; or to be stored in energy storage device 649 (e.g. a capacitor) forlater use.

Proximally located elements are electrically connected throughconductors. Distally located sensor 647, logic and control unit 648,energy storage device 649, and electrodes 650 and 644 are electricallyconnected through conductive elements. Variable intensity emitter 646transmits radiation at wavelength λ₂ (λ₂≠λ₁) off beam splitter 645 intowave-guide 643 and off beam splitter 910 to sensor 640. Preferably, thevariable intensity emitter 646 emits optical radiation when excited byan electrical potential, and is mounted upon a mirror to direct agreater percentage of emissions into wave-guide 643.

A preferred application of the embodiment illustrated in FIGS. 11 and 12uses electrodes 650 and 644 to capture electrical signals and directthem to logical and control unit 648 which delivers electrical energy toemitter 646 to emit optical radiation that is encoded with theelectrical signals received by electrodes 650 and 644. The encodedoptical signals are directed to beam splitter 645 and into wave-guide643 to sensor 640 that converts the encoded optical signal to an encodedelectrical signal. Output from sensor 640 is sent to logic and controlunit 638. This output is either utilized by logic and control unit 638to control the radiation from emitter 639, which is typically at a highenergy level (typically higher than radiation from emitter 646) and isused to stimulate distally located tissues and organs, or is relayed totransmitter 637 that relays this sensory information to externalsources.

In FIGS. 13 and 14, radiation emitter 651 transmits radiation,preferably optical radiation at wavelength λ₁ through beam splitter 652into wave-guide 655. This radiation exits wave-guide 656 at exit angle αand impinges upon sensor 657 that converts the radiation to electricalenergy. The electrical energy is used as previously described.Proximally and distally located elements are electrically connectedthrough conductors.

A second emitter 658 located on or within sensor 657 transmits radiationat wavelength λ₂ (λ₂≠λ₁) at cone angle β into wave-guide 656 to beamsplitter 652. The small size ‘d’ of emitter 658 relative to the largersize ‘D’ of sensor 658 and narrow radiation exit angle α and emissionangle β enable effective coupling of radiation from emitter 651 intosensor 657 and radiation from emitter 658 into wave-guide 656. Optionalcoupling lens 653 collects and directs radiation to sensor 654. Thedistally located light source may be a solid-state laser or lightemitting diode.

In FIGS. 15 and 16, radiation emitter 659 transmits radiation,preferably optical radiation at wavelength λ₁ and exit angle β₁ throughoptional coupling lens 661 into wave-guide 662. This radiation exitswave-guide 663 at exit angle α₁, and impinges upon sensor 664 thatconverts the radiation into electrical energy. The electrical energy isused as previously described.

A second emitter 665 located on or within sensor 664 transmits radiationat wavelength λ₂ at cone angle β₂ into wave-guide 663. This radiationexits wave-guide 662 at exit angle α₂ onto sensor 660. Ideally,wavelength λ₂≠λ₁ so that optical reflections from coupling lens 661 orwave-guide 662 do not interfere with radiation incident upon detector660. The small sizes ‘d’ of emitters 659 and 665 relative to the largersizes ‘D’ of sensors 660 and 664, combined with narrow radiation exitangles α₁ and α₂, and β₁ and β₂, enable effective coupling of radiationinto wave-guide (662, 663), and sensors 660 and 664.

In FIGS. 17 and 18, radiation emitter 666 transmits radiation,preferably optical radiation at wavelength λ₁ into wave-guide 667. Thisradiation exits wave-guide 670 and impinges upon sensor 671 thatconverts the radiation into electrical energy. The electrical energy isused as previously described.

A second distally located emitter 672 transmits radiation at wavelengthλ₂ into wave-guide 673. This radiation exits wave-guide 668 ontoproximally located sensor 669. Wavelength λ₂ may or may not be equal towavelength λ₁. Light sources 666 and 672 include a solid-state laser orlight emitting diode. Wave-guides (667, 670) and (668, 673) arepreferably included in the same lead assembly.

In FIGS. 19 and 20, a sensor 678 transparent to certain wavelengths ofoptical radiation is used. Radiation emitter 677 transmits radiation,preferably optical radiation at wavelength λ₁ through sensor 678 that istransparent to wavelength λ₁ into wave-guide 679 and exiting at exitangle α to sensor 682 that converts the radiation to electrical energy.The electrical energy is used as previously described.

A second emitter 681 located on or within sensor 682 transmits radiationat wavelength λ₂ (λ₂≠λ₁) at cone angle β into wave-guide 680 toproximally located sensor 678 where it is absorbed and converted intoelectrical energy. As before, the small size ‘d’ of emitter 681 relativeto the larger size ‘D’ of sensor 682 and narrow radiation exit angle αand emission angle β enable effective coupling of radiation from emitter677 into sensor 682 and radiation from emitter 681 into wave-guide 680.

FIG. 50 illustrates another embodiment of the present invention in whicha hermetic housing is constructed to provide part of an electrodetermination pair 448. The electrode termination pair 448 includes acup-shaped structure (tip) 449 acting as a tip electrode and thehermetic housing 446 (ring) acting as a ring electrode. The tip 449 andthe ring 446 are both substantially cylindrical in shape, and preferablyhave the same wall thickness. Note that the tip 449 has a rounded noseportion and a base portion that is planar in cross-section. The ring 446has proximal and distal end portions that are both preferably planar incross section.

As shown in FIG. 51, the tip 473 and the ring 463 can be made from abody-compatible, non-ferromagnetic metal such platinum, titanium oralloy of platinum or titanium. As shown FIGS. 52 and 53, the tip (497,522) and the ring (487, 515) can be made of a non-metallic material,such as ceramic, and covered with electrically conductive coatings (495,520) and (480, 505), respectively. The difference between FIGS. 52 and53 is that all exposed surfaces of the tip 497 and the ring 487 arecoated in FIG. 52, whereas only the outer surface of the tip 522 and thering 515 are coated in FIG. 53.

If a ceramic is used to form the tip and the ring, the material used ispreferably a suitable biocompatible ceramic material such a ceramic ofthe type commonly used for joint prostheses. By way of example only,such material is available from Ceramic Components Inc. of Latrobe, Pa.To form a ceramic tip and ring, ceramic slurry can be formed into thedesired shapes and fired to bake the ceramic material.

The electrically conductive coatings (495, 520) and (480, 505) arepreferably formed by very thinly coating the tip and the ring, as byelectroplating, sputtering or other deposition technique, etc., with asuitable metal. To facilitate MRI compatibility, the metal preferablyhas low magnetic susceptibility, such as titanium, platinum, an alloy oftitanium or platinum, or the like. Preferably, the coatings (495, 520)and (480, 505) are applied as thin as possible to achieve the twin goalsof efficient electrical interaction with implanted tissue whileminimizing interaction with MRI induced electromagnetic fields. By wayof example, the thickness of the coatings (495, 520) and (480, 505) mayrange from mono-molecular thickness to sub-micron or micron levelthickness.

FIGS. 50 through 53 show the electrode termination pair (448, 469, 498,524) being mounted to the distal end of a photonic catheter (451, 476,501). The tip and the ring are also interconnected by a short insulativestub (447, 468, 493, 518) that is solid, generally cylindrical in shape,and made from silicone, polyurethane, polyethylene, or any othersuitable biocompatible electrically insulating material. The outsidediameter of the stub preferably equals the outside diameter of the tipand the ring, to facilitate efficient implantation and removal in apatient. The ends of the stub can be bonded to the tip and the ringusing a suitable medical adhesive. To provide additional connectionintegrity, the stub can be formed with end portions (470, 492, 519) ofreduced diameter. One end portion of the stub is received into anopening (471, 494) in the base portion of the tip and bonded therein.The other end portion of the stub is received into an opening (459, 485,509) in the distal end of the ring and bonded therein.

The completed tip/ring assembly can be mounted to the distal end of thephotonic catheter in similar fashion. In particular, the photoniccatheter will be a generally cylindrical element whose exterior sheath(451, 474, 459) is made from silicone, polyurethane, polyethylene, orany other suitable biocompatible electrically insulating material. Notethat the sheath could be tubular in shape, with a small center borecarrying one or more optical conductors therein. Alternatively, thesheath could be formed around the optical conductors such that theconductors are embedded, in the material of the sheath

In either case, the outside diameter of the sheath will preferably bethe same as that of the ring and can be bonded thereto using a suitablemedical adhesive. To provide additional connection integrity, the sheathmay be formed with a small end portion (453, 477, 502) of reduceddiameter that is snugly received within an opening (454, 478, 503) inthe proximal end the ring and bonded therein.

Since the ring functions as a hermetically sealed component housing, itmust be provided with hermetically sealed closures at or near the endsthereof. These closures may be provided by a pair of closure walls (465,488, 516) and (461, 482, 513) that are secured within the interior ofthe ring. The closure walls can be formed from any suitablebio-compatible material capable of sealing the ring interior, includingmetals, polymers, and potentially other materials. To facilitate thesecure hermetic attachment of the closure walls, the inside of the ringcan be formed with a pair of recessed annular shoulders (456, 479, 504).

There may be disposed within the ring any number of components fordelivering electrical signals to, or sensing biological activity in, abody. Such components are collectively shown as a component array byreference numeral (462, 486, 514), and may include opto-electricaltransducers, electro-optical transducers, signal processors andamplifiers, digital microprocessors, temperature sensors, R-wavesensors, partial oxygen sensors, and any number of other components. Toprovide electrical interaction with surrounding body tissue, a positiveterminal of the component array is connected to a short metallic lead(457, 483, 507) made from copper or other suitable material of lowmagnetic susceptance.

In FIG. 51, the lead 457 is electrically connected to the ring byattaching it, as by soldering or the like, directly to the ring itself.In FIG. 52, the metallic lead 483 is electrically connected to the ringby attaching it, as by soldering or the like, to an interior portion ofthe metallic coating 480. In FIG. 53, the metallic lead 507 is fedthrough a small hole 506 in the wall of the ring so that it may beattached to the exterior metallic coating 505, as by soldering or thelike.

A negative terminal of the component array connects to a longer metalliclead (466, 489, 517) that is also made from copper or other suitablematerial of low magnetic susceptance. This metallic lead feeds through ahermetic seal terminal (464, 490, 511) mounted on the closure wall. Thismetallic lead then extends through the material of the stub (which canbe molded around the lead) and into the tip.

In FIG. 51, the metallic lead is electrically attached, as by solderingor the like, directly to the tip itself. In FIG. 52, the metallic leadis electrically attached, as by soldering or the like, to an interiorportion of the metallic coating. In FIG. 53, the metallic lead is fedthrough a small hole 523 in the ceramic wall of the tip so that it maybe attached to the metallic coating, as by soldering or the like.

When the tip and the ring are implanted in a patient's heart, the tipwill typically be embedded in the endocardial tissue, while the ring issituated in the right ventricle, in electrical contact with theendocardium via the ventricular blood. If the photonic catheter isconnected to a pacemaker, an optical pulse emanating from a photonicpacemaker pulsing unit (not shown) is sent down a fiber optic element orbundle of the photonic catheter. The fiber optic element or bundlepasses into the hermetically sealed interior of the ring via a hermeticseal terminal (460, 481, 512). There, the fiber optic element or bundledelivers the optical pulse to the component array, which preferablyincludes a photodiode array. The photodiode array produces an electricalimpulse that negatively drive the tip with respect to the ring at apotential of about 3-4 volts and a current level of about 3 milliampsfor a total power output of about 10 milliwatts. Note that a sensingfunction could be added by incorporating an electro-optical transducerinto the component array. Electrical sense signals would then beconverted to optical signals and placed on the fiber optic element orbundle for delivery to a sensing unit (not shown).

FIG. 54 illustrates an exemplary construction of the component array inwhich the array comprises a photodiode array 532 for receiving opticalpacing signals from the fiber optic element or bundle 525 and a lightemitting diode 533 for delivering optical sensing signals to the fiberoptic element or bundle. The components 532 and 533 are mounted on acircuit substrate 527 that is electrically connected to an electricalcircuit unit 534 that may include transducers, amplifiers, oscillators,a microprocessor, and other devices that can assist electrical pulsedelivery and biological sensing functions.

FIGS. 55 through 57 include a modified hermetic housing to provide aunitary or integral electrode termination pair 540. The electrodetermination pair 540 includes a tip 539 and a ring 538 that areconstructed as metallic coatings formed on the hermetic housing (551,565).

An electrically conductive coating (552, 566) formed at the distal endof the housing provides the tip. An electrically conductive coating(547, 559) formed at the proximal end of the housing provides the ring.

FIGS. 56 and 57 also show that the component array can be hermeticallysealed within the housing via the hermetic seal. The proximal end of thehousing may then be secured to the distal end of the photonic catheter,and the fiber optic element or array can be connected to the componentarray via the hermetic terminal. The component array is electricallyconnected to the tip and the ring via electrical leads.

FIG. 58 shows an exemplary implementation of the component array withinthe housing. This component array configuration is identical to thecomponent array configuration of FIG. 55.

In FIG. 59, a modified hermetic housing again provides a completeelectrode termination pair 586. The electrode termination pair 586includes a tip electrode 584 and a ring electrode 582 that areconstructed as electrically conductive band coatings on the hermetichousing, which is designated by reference numeral 581. A shallow well562 of FIG. 60 formed near the distal end of the housing 560 of FIG. 60may be used to mount the tip 561. A shallow well 593 of FIG. 60 formedtoward the proximal end of the housing 560 of FIG. 60 may be used tomount the ring 594 of FIG. 60.

FIG. 61 shows an exemplary implementation of the component array withinthe housing. This component array configuration is identical to thecomponent array configuration of FIG. 54.

The output of a typical pacemaker is illustrated in FIG. 31, which is agraph of the electrical direct current voltage (vDC) applied to theelectrode or electrodes at the distal end of a cardiac pacemaker lead,as a function of time. The indicated voltage of 3 vDC is a nominal valueand is typically often selected by the physician based on the type ofcardiac anomaly being corrected, the physical state of the patient'sheart, and other factors. However, it should be understood that thisvalue is intended to have a safety factor of two built into it; thus thetypical voltage required to pace the heart is 1.5 volts direct current,or less.

Referring again to FIG. 31, and noting that the time axis is not toscale, the typical time between pacing events is nominally one second,or 1000 milliseconds (mS). In normal practice, using modem pacemakers,this time interval is not fixed but is variable based upon two factors.The first factor is whether or not the heart requires pacing in order tobeat. The term ‘demand pacemaker’ applies to a device that senses heartactivity electrically and does not send a pacing signal to theelectrodes if the heart is beating on its own in a manner determined tobe acceptable by the computer controller within the device, and basedupon input programmed by the physician. Thus, during the time after therefractory period associated with the previous heartbeat ends 321, andup to a time when the next heartbeat is required 322, the pacemakerelectrode is used to sense heart activity and to disable the next pacingsignal 323 if the heartbeat is regular.

The second factor associated with demand pacing is physiologic demand;modern pacemakers are designed with additional sensing and analyticalcapability that permits the device to monitor physiologic demandassociated with physical activity or other forms of stress that wouldresult in an elevated heartbeat in a normal human subject. In responseto this heightened physiologic demand, the pacing signal 323 would begenerated at an earlier time than the 1000 mS delay indicated in FIG.31.

FIG. 32 is an expanded view similar to FIG. 31, showing the pacingsignal 326 over the nominal one-millisecond time interval of the actualpacing signal. The beginning of the pacing signal (319, 324) and the endof the pacing signal (320, 325) are shown in both FIG. 31 and FIG. 32for reference. Note that there is no other activity in this onemillisecond time interval; more particularly there is no attempt tosense heart activity nor the heart's response to the pacing signalduring the time pacing time interval between times (319, 324) and (320,325). This is in part due to the fact that while a relatively modestvoltage (about 3 volts) is being applied to the heart cardiac tissue bythe electrodes, the voltages sensed by the pacemaker in monitoring heartactivity (typically in the millivolt range) would be immeasurable usingtraditional techniques. In addition, the tissues surrounding the pacingelectrode develop a polarization potential in response to the energy inthe pacing signal; this serves to make measurements of heart activityvia those same electrodes very difficult using traditional techniques.However, the interval between times (319, 324) and (320, 325) is verylong in the context of modem computational electronic devices.

FIGS. 33, 34, and 35 are schematic representations of a cardiacpacemaker lead (327, 329, 333) having various electrode configurations.

In one preferred embodiment, and referring to FIG. 33, pacemaker lead327 comprises one or more electrical conductors communicating from aconnector on the body of the pacemaker device (not shown) to theelectrodes 328 that are affixed by one of a number of techniques to thesensitive cardiac tissue that initiates the natural heartbeat and thatis paced when necessary by the implanted pacemaker system. Theconfiguration shown in FIG. 33 is for a bipolar pacemaker; the positiveand negative terminals for electron flow through the cardiac tissue arethe two electrodes 328. It should be noted that there is an alternativeconfiguration referred to as unipolar, and it is not shown in thisfigure. In the case of a unipolar configuration, there is a singleelectrode 328 at the heart; the return path for electron flow is throughthe general bulk tissue back to the case of the device itself. In eitherunipolar or bipolar configurations, electrodes 328 are used both to pacethe heart during the period between times (319, 324) and (320, 325)shown in FIGS. 31 and 32, but are also used to sense heart activityelectrically between times 321 and 322 shown in FIG. 31.

In the embodiment depicted in FIG. 34, sensing electrode 332 is disposedat a distance of at least about 5 millimeters from pacing electrode 330in order to provide a degree of electrical isolation between tissuesthat will develop a polarization potential and tissues being sensed forheartbeat activity. Similarly, in the embodiment depicted in FIG. 35,sensing electrode pair 335 is disposed at a distance of at least about 5millimeters from pacing electrode pair 334.

In another preferred embodiment, cardiac pacemaker lead is not anelectrical conductor but rather comprises one or more optical fibersthat carry light energy between the pacemaker device case and theelectrodes. This embodiment may be used in order to create pacemakerleads that are immune to the intense radio frequency and magnetic fieldsassociated with magnetic resonance imaging (MRI) and which fields can insome cases result in damage to the pacemaker and/or injury or death tothe pacemaker patient who inadvertently undergoes MRI diagnosis. In thisembodiment electrodes are more complex than in the former embodiment;for purposes of pacing they comprise a photodiode (not shown) used toconvert light energy to electrical energy within them, and in the caseof sensing cardiac activity they also comprise a miniature electricalamplifier and light emitting diode source that creates an optical signalthat travels from the electrode back to a pacemaker device that uses thephotonic catheter of this embodiment.

In another embodiment, and referring to FIG. 34, the pacemaker lead 329connects the pacemaker device case (not shown) to a set of electrodes330, 331, and 332 at its distal end and affixed to cardiac tissue as inthe previous embodiment. Electrode 331, as in the previous embodiment,is capable of either pacing the heart or sensing heart activityelectrically. Electrode 330 is used only to pace the heart, and isidentical in its function to that part of the function of thedual-purpose electrode. In like manner electrode 332 is used only forsensing heart activity electrically, in a fashion identical to that partof the function of the dual-purpose electrode.

The reason for the configuration shown in FIG. 34 is that the cardiactissue immediately involved in the pacing event, and which develops apolarization potential as a result of the pacing signal, is somewhatremoved physically from the cardiac tissue immediately around thesensing electrode 332, thus providing some degree of isolation frompolarization potential in the area where cardiac sensing is being done,but still providing ample opportunity for sensing any cardiac activity.Thus this embodiment provides the opportunity for sensing measurementsto be made during dwell periods in the overall pacing signal wherein novoltage is being applied to the cardiac tissue.

In a further embodiment, and still referring to FIG. 34, pacemaker lead329 does not contain electrical conductors but rather comprises one ormore optical fibers, as described in a previous embodiment. Likewise,electrodes 330 and 331 have the capability to convert optical energy toelectrical energy in order to pace the heart, and electrodes 331 and 332comprise electrical amplifier and electricity-to-light conversion, as isalso described in the previous embodiment.

In yet another preferred embodiment, shown in FIG. 35, pacemaker lead333 connects the pacemaker device case (not shown) to a set ofelectrodes 334 and 335 at its distal end and is affixed to cardiactissue as in the previous embodiments. In this embodiment, additionalseparation between the volume of cardiac tissue being paced (betweenelectrodes 334) and the volume of cardiac tissue being sensed (betweenelectrodes 335) is created in order to provide further improvements inelectrical isolation between those areas, thereby providing furtherimprovement in the ability to make sensing measurements during cardiacpacing.

In yet another embodiment, and still referring to FIG. 35, pacemakerlead 333 does not contain electrical conductors but rather one or moreoptical fibers, as described in a previous embodiment. Likewise,electrodes 334 have the capability to convert optical energy toelectrical energy in order to pace the heart, and electrodes 335comprise electrical amplifier and electricity-to-light conversion asalso described in previous embodiments.

In one preferred embodiment of the present invention, a technique ofpulsewidth modulation is used to pace the heart and to provide theopportunity for real-time measurement of cardiac tissue activity.

Referring to FIG. 36, it may be seen that a pacing signal 338 thatbegins at time 341 is not a traditional square wave pulse as shown inFIGS. 31 and 32, but is a series of much faster pulses that apply avoltage 337 for a time period 339 and that apply no voltage during timeperiod 340.

For example, if time period 339 is chosen to be two microseconds and iftime period 340 is chosen to be one microsecond, a single repeat ofsequence 339 and 340 has a duration of three microseconds. If thissequence is repeated three hundred thirty-three times, the time intervalfor pulse 338 will be about one millisecond, corresponding to the timeinterval of a single traditional pacing signal to the heart. Forpurposes of this illustrative example and again referring to FIG. 36,voltage 337 may be chosen to compensate for the fact that no voltage isapplied for one third of the time. In order for a pulsewidth signal 338having 66% duty cycle as described in this illustration to deliver thesame amount of electrical energy to the cardiac tissue as in a squarewave 3 volt DC pulse of 1 millisecond duration, and taking intoconsideration the relationship of energy to voltage in a purelyresistive medium (energy is proportional to the square of the appliedvoltage), the voltage 337 will be chosen to be 3 volts DC multiplied bythe square root of 1.5, or 3.67 volts direct current. If the frequencyof pulsewidth modulated pacing curve 338 is high with respect to thereaction time of cardiac tissue, that tissue will react in the samemanner to the pulsewidth modulated signal having 66% duty cycle and 3.67volt peak signal level as it would to a square wave of the same durationat 3.0 volt.

The foregoing example is intended to be illustrative only; in theembodiment depicted, time periods 339 and 340 may range from below 1microseconds to over 100 microseconds in order to optimize the responseof the system to design choices in the pacemaker device or the pacemakerlead and electrodes. In addition, this embodiment provides for timeperiods 339 and 340 to be variable over time, both in absolute durationand in their ratio. Further, the applied voltage 337 may be variableover time within a single pacing signal 338, or between pacing signals,as a function of changes in physiologic demand or based on changes inprogrammed response of the pacemaker system. For purposes of thisspecification, the overall signal that spans between times 339 and 340will be referred to as the pacing signal, the shorter signals sent tothe heart in multiples will be referred to as pulses, and the muchshorter signals described in this illustrative example as having timeduration 339 will be referred to as micropulses.

Referring once again to FIG. 36, it may be seen that a cardiac tissuesensing measurement 343 may be carried out during time period 342. Inone embodiment, time period 342 may occur any time during the pacingsignal and may have any duration appropriate to making said sensingmeasurement. In a preferred embodiment, time period 342 is selected tobe shorter in duration than time period 340, and is further synchronizedso as to fall within time period 340. The result is that the electricalmeasurement of cardiac tissue activity is done during a time periodwherein there is not pacing signal applied to the tissue.

Referring again briefly to FIGS. 33, 34, and 35, it may be seen that incombination with the placement of electrodes on pacemaker lead thatprovides isolation between the tissue being paced and the tissue beingsensed, the additional temporal isolation of sensing period from theactive time period of the pulsewidth modulated pacing signal, a means isprovided to measure the onset of cardiac response to the pacing signalwhile the signal is still being generated as a set of multiple shorterpulses.

FIG. 37 is a graph depicting the operation of one preferred embodimentthat gains energy efficiency by means of early termination of the pacingsignal, but which uses a constant voltage applied to the micropulsescomprising the pacing signal. The peak voltage of pulses that make uppacing signal 345 rises from zero to voltage 344 at time 346, aspreviously shown in FIG. 36. At time 348, when a signal from heartcauses cessation of the micropulsing process, the pulsewidth pacingsignal 345 returns to zero until the next pacing signal is commandedfrom the demand controller. The area 347 depicts the additional signalthat a traditional pacemaker not practicing pulsewidth pacing would sendto pace the heart after the onset of a beat at time 348. As discussedpreviously, standard clinical practice calls for a threefold safetyfactor in pulse duration; employing a pacemaker in a manner depicted inFIG. 37, would result in up to approximately a 65 percent reduction inenergy consumption for the pacemaker system.

FIG. 38 is a graph depicting the operation of another preferredembodiment that gains energy efficiency by means of both earlytermination of the pacing signal and by the additional use of gradientpulsewidth power control. As in the previous embodiment, pulsewidthpacing signal 352 begins to rise from zero at time 353, and the voltageof each of the micropulses rises with each micropulse cycle. FIG. 38depicts a linear rise with time, but experimentation may result in adifferent algorithm that better matches the electrochemistry of cardiactissue; thus FIG. 38 should be considered as illustrative of a varietyof waveforms that may be employed to excite the heart. At time 354, whena signal from heart causes cessation of the micropulsing process, thepulsewidth pacing signal 352 returns to zero until the next pacingsignal is commanded from the demand controller. As in the example ofFIG. 37, the area 356 depicts the signal that a traditional pacemakernot practicing pulsewidth pacing would send to pace the heart.

As discussed previously, standard clinical practice calls for athreefold safety factor in pulse duration. The typical twofold safetyfactor in applied voltage results in a power level that is four timeshigher than the minimum to pace the specific patient's heart. Thus incombination the joint safety factors applied to voltage and pulseduration result in an energy utilization that is twelve times higherthan the minimum needed to reliably pace that individual's heart. Bypracticing pulsewidth pacing, which permits the cessation of thepulsewidth pacing signal virtually the instant the heart begins to beat,the energy consumption of a pacemaker may be reduced by as much as 90%.

It should also be understood that in using a pulsewidth modulationcontrol technique, it is not necessary to alter the actual peak voltageof the pulses that make up the pacing signal to effect an apparentchange in applied voltage. If the frequency of the pulses is high enoughin comparison to the response time of the circuit and the cardiac tissuethrough which the pacing signal is conducted, the tissue will react inthe same manner as if the applied voltage were the actual peak voltagemultiplied by the duty cycle. Thus, the electronic circuit may bedesigned to utilize a single voltage and adjust duty cycle by adjustingthe ratio of times 339 and 340. This permits optimization the energyefficiency of power sources and switching circuits.

FIG. 39 depicts an alternative overall waveform for pacing signal 360.Note that for reasons of simplicity the overall value of peak voltage isshown for pacing signal 360, and not the individual pulsewidths, asshown in FIG. 38. However, this embodiment still makes use of thehigh-frequency pulsewidth approach shown in greater detail in FIGS. 37and 38. Whereas FIG. 38 depicts a linear rise with time, FIG. 39 depictsan initial rise of pacing signal 360 at time 361 from 0 vDC to voltage359, followed by a nonlinear increase to voltage 358, at which time 362a heartbeat has been sensed, and pacing signal 360 is cut off as in theprevious embodiments described herein.

Experimentation may result in a different algorithm that better matchesthe electrochemistry of cardiac tissue, and this algorithm may bedeveloped for the specific patient during the initial post-implantationperiod. Thus, FIGS. 38 and 39 should be considered as illustrative of avariety of waveforms that may be employed to excite the heart, and maybe made specific to the needs of each pacemaker patient.

As in the previous embodiment depicted in FIG. 38, the use of pulsewidthmodulation techniques in the embodiment depicted in FIG. 39 permitsoptimization of energy efficiency by adjusting duty cycle rather thanadjusting actual peak voltage.

The photonic catheter described above may be used for transmission of asignal to and from a body tissue of a vertebrate. The fiber optic bundlehas a surface of non-immunogenic, physiologically compatible materialand is capable of being permanently implanted in a body cavity orsubcutaneously. The fiber optic bundle has a distal end for implantationat or adjacent to the body tissue and a proximal end. The proximal endis adapted to be coupled to and direct an optical signal source, and thedistal end is adapted to be coupled to an optical stimulator. The fiberoptic bundle delivers an optical signal intended to cause an opticalstimulator coupled to the distal end to deliver an excitatory stimulusto a selected body tissue, such as a nervous system tissue region; e.g.,spinal cord or brain. The stimulus causes the selected body tissue tofunction as desired.

The photonic catheter further includes a photoresponsive device forconverting the light transmitted by the fiber optic bundle intoelectrical energy and for sensing variations in the light energy toproduce control signals. A charge-accumulating device receives andstores the electrical energy produced by the photoresponsive device. Adischarge control device, responsive to the control signals, directs thestored electrical energy from the charge-accumulating device to acardiac assist device associated with a heart.

The photoresponsive device may include a charge transfer control circuitand a photodiode. The charge transfer control circuit controls adischarging of a photodiode capacitance in two separate dischargeperiods during an integration period of the photodiode such that a firstdischarge period of the photodiode capacitance provides the sensing ofvariations in the light energy to produce control signals and a seconddischarge period of the photodiode capacitance provides the convertingthe light transmitted by the photonic lead system into electricalenergy. The first discharge period can be a shorter time duration thatthe time duration of the second discharge period. During the firstdischarge period, a control signal sensing circuit is connected to thephotodiode, and during the second discharge period, thecharge-accumulating device is connected to the photodiode. Thecharge-accumulating device may be a capacitor or a rechargeable battery.

The photonic catheter can also transmit between the primary devicehousing and the cardiac assist device, both power and control signals inthe form of light. A photoresponsive device converts the lighttransmitted by the photonic lead system into electrical energy and tosense variations in the light energy to produce control signals. Acharge-accumulating device receives and stores the electrical energyproduced by the photoresponsive device, and a discharge control device,responsive to the control signals, directs the stored electrical energyfrom the charge-accumulating device to the cardiac assist deviceassociated with the heart.

The photoresponsive device, in this embodiment, may include a chargetransfer control circuit and a photodiode. The charge transfer controlcircuit controls a discharging of a photodiode capacitance in twoseparate discharge periods during an integration period of thephotodiode such that a first discharge period of the photodiodecapacitance provides the sensing of variations in the light energy toproduce control signals and a second discharge period of the photodiodecapacitance provides the converting the light transmitted by thephotonic lead system into electrical energy. The first discharge periodcan be a shorter time duration that the time duration of the seconddischarge period. During the first discharge period, a control signalsensing circuit is connected to the photodiode, and during the seconddischarge period, the charge-accumulating device is connected to thephotodiode. The charge-accumulating device may be a capacitor or arechargeable battery.

The physical realization of the photodiode functions as light-detectingelements. In operation, the photodiode is first reset with a resetvoltage that places an electronic charge across the capacitanceassociated with the diode. Electronic charge, produced by the photodiodewhen exposed to illumination, causes charge of the photodiodecapacitance to dissipate in proportion to the incident illuminationintensity. At the end of an exposure period, the change in photodiodecapacitance charge is collected as electrical energy and the photodiodeis reset.

Manipulating or adjusting the charge integration function of thephotodiode can modify the creation of energy by the sensors. Chargeintegration function manipulation can be realized by changing of anintegration time, T_(int), for the photodiode. Changing the integrationtime, T_(int), changes the start time of the charge integration period.

Integration time, T_(int), is the time that a control signal is not setat a reset level. When the control signal is not at a reset value, thephotodiode causes charge to be transferred or collected therefrom. Thetiming of the control signal causes charge to be transferred orcollected from the photodiode for a shorter duration of time or longerduration of time. This adjustment can be used to manage the charge inthe photodiode so that the photodiode does not become saturated withcharge as well as to manage the current output of the sensor.

Another conventional way of manipulating the charge integration functionis to use a stepped or piecewise discrete-time charge integrationfunction. By using a stepped or piecewise discrete charge integrationfunction, the charge in the photodiode can be further managed so thatthe photodiode does not become saturated with charge as well as tomanage the current output of the photodiode.

The photonic catheter can also be used to measure displacement current.Unlike a standard conduction current of moving electrons, displacementcurrent is a measure of the changing electric field in the air,generated by the shifting voltages on the skin surface. To accuratelymeasure this subtle current in the air without shorting it, a sensor isneeded with impedance higher than that of the air gap between the bodyand the sensor. Otherwise, the sensor will drain the electrical signaljust like an ECG contact sensor does. The sensor can be a small copperdisc about a centimeter across, which can produce sensitive ECGs.

As illustrated in FIGS. 66-69, a photonic catheter 585 may contain asensor to detect the presence of MRI insult. Most specifically, thephotonic catheter 585 may include at a distal end a logic and controlcircuit 586 connected to an amplifier 587. The amplifier 587 may beconnected to a single MRI coil as illustrated in FIG. 66 or to multipleMRI coils (589, 590, 591 . . . ) as illustrated in FIG. 67. In FIG. 68,the MRI insult sensor is encased in a sleeve 592 that enables the MRIcoil 592 to be rotatable within the photonic catheter 585. Lastly, thephotonic catheter 585, as illustrated in FIG. 69, may position two MRIcoils 593 and 594 at predetermined angles β to each other, such as 90°.The MRI coils are located in the distal end of the photonic catheter anddetects characteristics of magnetic radiation of a predetermined nature.Each coil may be designed to detect a different type of radiation.

FIG. 21 illustrates an optical transducer including a pressure sensor225 in a porous non-conductive insert 226 that is coupled to a photoniccatheter or other optical communication channel.

FIG. 22 illustrates in more detail, the pressure optical transducerdevice of FIG. 21. In FIG. 22, an optical transducer device is anchoredto a predetermined tissue region 230, such as a cardiac muscle region,by anchors 227 and 229. The anchors are connected to a porous sleeve 231that houses a pressure sensor 228. The optical transducer device furtherincludes a mechanical-optical transducer 232, within housing 233, toproduce an optical signal corresponding to the movement of pressuresensor 228. Pressure sensor 228 moves back and forth in response topressure generate by contractions of the predetermined tissue region230. Based on the pressure gradient produced, the pressure sensor 228will move and cause the mechanical-optical transducer 232 to produce asignal containing information on the characteristics of thepredetermined tissue region 230.

In FIG. 23, an optical transducer device is anchored to a predeterminedtissue region 234, such as a cardiac muscle region, by a porous sleeve235 that houses a pressure sensor 236. The optical transducer devicefurther includes a mechanical-optical transducer 239, within housing 237and connected to optical cable 238, to produce an optical signalcorresponding to the movement of pressure sensor 236. Pressure sensor236 moves back and forth in response to pressure generate bycontractions of the predetermined tissue region 234. Based on thepressure gradient produced, the pressure sensor 236 will move and causethe mechanical-optical transducer 239 to produce a signal containinginformation on the characteristics of the predetermined tissue region234.

In FIG. 24, an optical transducer device is anchored to a predeterminedtissue region 240, such as a cardiac muscle region, by a porous sleeve241 that houses an optical device 242. The optical device 242 producesan optical signal that reflects off the predetermined tissue region 240.Based upon the nature of the reflection, optical device 242 producesoptical signals corresponding to the characteristics of thepredetermined tissue region 240. These optical signals are transmittedover an optical cable 244 within a housing 243.

In FIG. 25, an optical transducer device for a cardiac region isillustrated. An optical device 251 produces light that is fed alongfiber optics 247 and 250 to a ventricle area of the heart and an atriumarea of the heart, respectively. The light is reflected off these areasand fed back to the optical device 251 through fiber optics 248 and 249.Based upon the nature of the reflection, optical device 251 producesoptical signals corresponding to the characteristics of the monitoredareas. These optical signals 252 are transmitted over an optical cable253 to a control unit device 254 at a proximal end of the optical cable253.

FIG. 26 illustrates one embodiment of an optical sensor. In FIG. 26, afiber optic bundle 258 includes individual fiber optics 259. One of thefiber optics produces the reference light that is reflected off flap 261within the optical sensor. The flap 261 will move between stops 257 and260 based on characteristics within a predetermined tissue region. Asthe flap 261 moves on pivot 262, the light is reflected at differentangles and thus is collected by a different fiber in the fiber opticbundle, depending upon the angle of reflection. In this way, thecharacteristics of the predetermined tissue region can be measured.

FIGS. 63 and 64 illustrate one embodiment of an optical sensor 1008. InFIGS. 63 and 64, a fiber optic bundle 1017 includes individual fiberoptics 1013 and 1016. One of the fiber optics 1013 produces thereference light that is reflected off flap 1014 within the opticalsensor 1008. The flap 261 will move based on muscle contractions ofmuscle tissue 1018 and 1020 in a predetermined tissue region that iswithin the optical sensor 1008 through openings 1010 and 1012. As theflap 1014 moves on pivot 1015, the light is reflected at differentangles and thus is collected by a different fiber 1016 in the fiberoptic bundle, depending upon the angle of reflection. In this way, thecharacteristics of the predetermined tissue region can be measured.

FIG. 62 is an optical sensor and stimulation device 1030 for a photoniccatheter. In FIG. 62, the optical sensor and stimulation device 1030includes a ring electrode 1034 and a tip electrode 1032 to sense orstimulate a predetermined tissue region. The ring electrode 1034 and atip electrode 1032 are connected to a control circuit 1038 that producesenergy to enable the ring electrode 1034 and tip electrode 1032 tostimulate the predetermined tissue region or enables the ring electrode1034 and tip electrode 1032 to sense characteristics of thepredetermined tissue region. Control signals from a proximal end arecommunicated along a fiber optic 1044 and received by sensor 1040.Sensor 1040 also receives other light signals over channel 1044 that isconverted into electrical energy to be stored for later use. The sensedcharacteristics of the predetermined region are transmitted by device1008 over fiber optic 1017 to the proximal end.

FIG. 65 illustrates a pressure pulse sensor 580. Cardiac tissue causes amirror membrane to be at position 578 when the heart is in the diastolicinterval because the pressure from the cardiac tissue decreases and inposition 579 when the heart is in the systolic interval because thepressure from the cardiac tissue increases. When the mirror membrane isin position 579, laser light 581 from fiber optic 583 is reflected alongray 582 to fiber optic sensor 584. The pressure is transferred to thepressure pulse sensor 580 through openings 576 and 577.

Alternatively to the electromagnetic insult immune systems describedabove, a system can avoid failure during magnetic resonance imaging bydetermining a quiet period for a tissue implantable device andgenerating a magnetic resonance imaging pulse during a quiet period ofthe tissue implantable device. Moreover, a system can avoid failure dueto an external electromagnetic field source by detecting a phase timingof an external electromagnetic field or external magnetic resonanceimaging pulse field and altering operations of the tissue implantabledevice to avoid interfering with the detected external electromagneticfield or external magnetic resonance imaging pulse field. In theseinstances the tissue implantable device may be a cardiac assist device.

The concepts of the present invention may also be utilized in anelectromagnetic radiation immune tissue invasive delivery system. Theelectromagnetic radiation immune tissue invasive delivery system has aphotonic lead having a proximal end and a distal end. A storage device,located at the proximal end of the photonic lead, stores a substance tobe introduced into a tissue region. A delivery device delivers a portionof the stored substance to a tissue region. A light source, in theproximal end of the photonic lead, produces a first light having a firstwavelength and a second light having a second wavelength.

A wave-guide is located between the proximal end and distal end of thephotonic lead. A bio-sensor, in the distal end of the photonic lead,senses characteristics of a predetermined tissue region, and a distalsensor, in the distal end of the photonic lead, converts the first lightinto electrical energy and, responsive to the bio-sensor, to reflect thesecond light back the proximal end of the photonic lead such that acharacteristic of the second light is modulated to encode the sensedcharacteristics of the predetermined tissue region. A proximal sensor,in the proximal end of the photonic lead, converts the modulated secondlight into electrical energy, and a control circuit, in response to theelectrical energy from the proximal sensor, controls an amount of thestored substance to be introduced into the tissue region.

In this embodiment, the sensed characteristic may be an EKG signal, aglucose level, hormone level, or cholesterol level. The stored substancemay be a cardiac stimulating substance, a blood thinning substance,insulin, estrogen, progesterone, or testosterone.

The MRI compatible photonic catheter, according to the concepts of thepresent invention, can also be utilized to illuminate a multiple sectorphotodiode, whose sectors are electrically connected in series so thatthe voltage output of each sensor is additive, thereby producing a totaloutput voltage in excess of what would be achieved from a single sensor.

In another embodiment of the present invention, a higher voltage andcurrent outputs is achieved by increasing the number and size ofdetectors. This embodiment also provides very accurate and stablealignment of the radiation wave-guide to the sensor, and a uniformspatial intensity of the output beam that illuminates the multiplesensor sectors.

An example of a MRI compatible photonic catheter being utilized totransfer power or energy to a tissue region located at a distal end ofthe catheter is illustrated in FIG. 70. FIG. 70 shows a wave-guide 2001coupled to a radiation source (not shown). The wave-guide 2001 directsradiation into a radiation scattering medium 2007. Attached to thesurface of the radiation scattering medium 2007 are multiple radiationsensors 2010-2013, mounted along the axis of scattering medium 2007, forreceiving and converting incident radiation into electrical energy. Themultiple radiation sensors 2010-2013 are electrically connected inseries so that the voltage output of each sensor is additive, therebyproducing a total output voltage in excess of what would be achievedfrom a single sensor.

The physical realization of the sensors is either a plurality ofphototransistors or a plurality of photodiodes functioning aslight-detecting elements. In operation, the sensor is first reset with areset voltage that places an electronic charge across the capacitanceassociated with the diode. Electronic charge produced by, for example, aphotodiode, when exposed to illumination, causes charge of the diodecapacitance to dissipate in proportion to the incident illuminationintensity. At the end of an exposure period, the change in diodecapacitance charge is collected as electrical energy and the photodiodeis reset.

Manipulating or adjusting the charge integration function of the sensorcan modify the creation of energy by the sensors. Charge integrationfunction manipulation can be realized by changing of an integrationtime, T_(int), for the sensor. Changing the integration time, T_(int),changes the start time of the charge integration period.

Integration time, T_(int), is the time that a control signal is not setat a reset level. When the control signal is not at a reset value, thesensor causes charge to be transferred or collected therefrom. Thetiming of the control signal causes charge to be transferred orcollected from the sensor for a shorter duration of time or longerduration of time. This adjustment can be used to manage the charge inthe sensor so that the sensor does not become saturated with charge aswell as to manage the current output of the sensor.

Another conventional way of manipulating the charge integration functionis to use a stepped or piecewise discrete-time charge integrationfunction. By using a stepped or piecewise discrete charge integrationfunction, the charge in the sensor can be further managed so that thesensor does not become saturated with charge as well as to manage thecurrent output of the sensor.

The radiation scattering medium 2007 and multiple sensors 2010-2013 aremounted such that there is little or no surface of the scattering mediumthat is not covered by a sensor. Any areas that are not covered bysensors are preferably covered with an internally reflective coatingthat directs incident radiation back into the scattering medium 2007 forabsorption by the sensors 2010-2013. Together these features ensure thatthe sensors 2010-2013 absorb a maximum amount of radiation.

In FIGS. 71 and 72, multiple sensors 2021-2026 are alternately mountedcircumferentially along the periphery of the scattering medium 2007, forreceiving and converting incident radiation into electrical energy. Themultiple radiation sensors 2021-2026 are electrically connected inseries so that the voltage output of each sensor is additive, therebyproducing a total output voltage in excess of what would be achievedfrom a single sensor.

In FIG. 73, radiation scattering medium 2031-2034 with a decreasingradiation transmission rate along the axis of the medium 2031-2034 isused. A scattering medium 2031-2034 with these properties would be usedwhen sensors 2035-2038 are electrically connected in series withconsecutive sensors in the electrical circuit placed further along theaxial direction of the scattering medium. This feature ensures that eachsensor receives an equal exposure of radiation, produces a similaroutput current, thereby ensuring that the output current of the seriescircuit including all sensors is not limited by the output current ofany individual sensor due to limited incident radiation.

In FIG. 74, multiple sensors 2041-2044 of varying size along the axis ofthe scattering medium 2007 are used. By placing larger sensors towardsthe distal end of the scattering medium 2007, these sensors 2043-2044receive an exposure of radiation equal to more proximally positionedsensors 2041-2042 and therefore produce equivalent output currents, eventhough the radiation intensity at the distal end of the scatteringmedium 2007 may be less than the radiation intensity at the proximal endof the scattering medium 2007.

In FIG. 75, a wave-guide 2001 is coupled to a radiation source (notshown) to direct radiation into a second wave-guide 2054 with multipleradiation beam splitters 2050-2053 located along the optical axis of thewave-guide. Attached to the second wave-guide 2054 are multipleradiation sensors 2045-2048, mounted along the axis of the wave-guide2054, for receiving and converting incident radiation into electricalenergy. The multiple radiation sensors 2045-2048 are electricallyconnected in series so that the voltage output of each sensor isadditive, thereby producing a total output voltage in excess of whatwould be achieved from a single sensor. The multiple sensors 2045-2048are mounted such that there is little or no surface of the secondwave-guide 2054 that is not covered by either a sensor or internallyreflective coating. Together these features ensure that the sensors2045-2048 absorb a maximum amount of radiation.

In FIG. 76, a second wave-guide 2059 with beam splitters that havedecreasing radiation transmission rates along the axis of the medium2059 is used. This feature would be used when sensors 2055-2058 areelectrically connected in series with consecutive sensors in theelectrical circuit placed further along the axial direction of thewave-guide 2059. Each sensor receives an equal exposure of radiation andproduces a similar output current, thereby ensuring that the outputcurrent of the series circuit including all sensors is not limited bythe output current of any individual sensor due to limited incidentradiation.

In FIG. 77, a wave-guide 2001 is coupled to a radiation source (notshown) to direct radiation onto a stack of sensors 2061-2064 such thateach sensor absorbs a fraction of radiation incident upon the stack. Themultiple radiation sensors 2061-2064 are electrically connected inseries so that the voltage output of each sensor is additive, therebyproducing a total output voltage in excess of what would be achievedfrom a single sensor. To ensure maximum current output of the seriescircuit containing all sensors 2061-2064, the radiation capture isincreased with increasing distance into the sensor stack, which can beaccomplished in several ways, including increasing sensor thickness thatreduces radiation transfer through the consecutive sensors.

In FIG. 78, a wave-guide 2001 is coupled to a radiation source (notshown) to direct radiation onto a concentrically oriented array ofsensors 2071-2073. Multiple radiation sensors 2071-2073 are electricallyconnected in series so that the voltage output of each sensor isadditive, thereby producing a total output voltage in excess of whatwould be achieved from a single sensor. Each sensor has an equal area toensure equal radiation exposure to all sensors 2071-2073, therebyproducing maximum current output for the series connected sensor array.This embodiment would be used when it is desirable to over-illuminatethe sensor array to ensure equal radiation exposure to all sensors.

In FIG. 79, a wave-guide 2001 is coupled to a radiation source (notshown) to direct radiation onto a reflective grating 2084 that dispersesradiation uniformly over the surface of multiple concentrically locatedsensors 2081-2083. The multiple radiation sensors are electricallyconnected in series so that the voltage output of each sensor isadditive, thereby producing a total output voltage in excess of whatwould be achieved from a single sensor.

In FIG. 80, a wave-guide 2001 is coupled to a radiation source (notshown) to direct radiation onto a single radiation sensor 2091 that isconnected to multiple capacitors (C₁, C₂, C₃, . . . , C_(n))electrically connected in parallel, enabling simultaneous charging ofthe capacitors (C₁, C₂, C₃, . . . , C_(n)) by the output voltage of thesingle sensor 2091. The voltage of each capacitor is controlled by theduration of the single pulse of radiation incident upon the singlesensor.

In FIG. 81, the charged capacitors (C₁, C₂, C₃, . . . , C_(n)) areswitchable to a series electrical circuit so that the voltage output ofeach capacitor is additive, thereby producing a total output voltage inexcess of what would be achieved from a single capacitor.

In FIG. 82, a catheter features a solid-state control circuit 2094 tomanage capacitor charging, switching, and discharging functions, as wellas other distal control functions. The control circuit 2094 is poweredby electrical energy supplied by the illuminated sensor 2091. Additionalfeatures of this illustrated catheter include a housing and pacingelectrodes 2093 and 2095.

Variable capacitance capacitors can be utilized that are tuned toprecisely match individual capacitor capacitances, thereby providingextraordinary control over output voltage and power.

In FIGS. 81 and 82, the parallel electrical circuit ensures that eachcapacitor is charged to the same voltage level, ensuring a predictableoutput voltage when the parallel charged capacitors are connected inseries and discharged. Moreover, the absence of multiple sensor sectorsensures that spatial variation in illumination intensity between sectorswill not minimize the current of any one sector and thereby the entirecircuit. Furthermore, the total energy dissipated by the seriesconnected electrical circuit is determined by parameters that are easyto control; such as, the pre-selected capacitance of the capacitors(Power=CV²/2), as well as the intensity and duration of the radiationpulse and duration of the discharge pulse which are controlled by thesolid state control circuit. The diameter of the single sensor 2091 islimited only by the size of the radiation wave-guide 2001. Lastly,reliability is improved due to reduced switching operations.

In FIG. 83, a wave-guide 2001 is coupled to a radiation source (notshown) to direct radiation onto a single radiation sensor 2091 that issequentially connected to multiple capacitors (C₁, C₂, C₃, . . . ,C_(n)) for charging. The voltage of each capacitor is controlled by theduration of the radiation pulse incident upon the surface of the singlesensor 2091.

In FIG. 84, the capacitors (C₁, C₂, C₃, . . . , C_(n)) are subsequentlyconnected in series for discharging, thereby producing a total outputvoltage in excess of what would be achieved from a single sensor orsingle capacitor. A solid-state control circuit (not shown) is utilizedto manage capacitor charging, switching, and discharging functions, aswell as other distal control functions. The control circuit is poweredby electrical energy supplied by the sensor 2091.

The electrical measurements of the charging characteristics of eachcapacitor are determined prior to utilizing the catheter. Thiscalibration information is then pre-programmed into a proximally locatedcontrol circuit to determine the duration and intensity of the radiationpulse required to achieve a specific voltage across the capacitor,thereby providing a predictable output voltage when the parallel chargedcapacitors are connected in series and discharged.

In FIGS. 83 and 84, the sequentially charging electrical circuit enableseach capacitor to be charged with a pre-determined pulse intensity andduration, ensuring a predictable output voltage when the parallelcharged capacitors are connected in series and discharged. The absenceof multiple sensor sectors ensures that spatial variation inillumination intensity between sectors will not minimize the current ofany one sector and thereby the entire circuit. Furthermore, the totalenergy dissipated by the series connected electrical circuit isdetermined by parameters that are easy to control; such as, thepre-selected capacitance of the capacitors (Power=CV²/2), as well as theintensity and duration of the radiation pulse and duration of thedischarge pulse which are controlled by the solid state control circuit.The diameter of the sensor 2091 is limited only by the size of theradiation wave-guide 2001.

In FIG. 85, the output energy of a single radiation source 3001 is splitinto multiple beams by radiation beam splitter 3006 having multiple beamsplitters 3002-3005 and directed into multiple wave-guides 3007-3010 todirect radiation onto multiple radiation sensors 3011-3013. Redundantsensors 3011-3013 are connected in series to produce a total outputvoltage in excess of what would be achieved from a single sensor.

Power transfer can also be realized by a radiation source coupled to awave-guide to direct radiation onto a single radiation sensor. Thisphotonic system design is repeated with additional radiation sources,additional wave-guides, and additional radiation sensors. Redundantsensors are connected in series to produce a total output voltage inexcess of what would be achieved from a single sensor.

These embodiments may also utilize a variable intensity radiation sourcethat can be used to vary the output current of the series connectedsensors. Moreover, this embodiment may include a control circuit thatcontrols the period and nature of the charge integration function of thesensors to maximize the output current of the sensors.

It is noted that the power transfer embodiments illustrated in FIGS.70-85 can be combined with the photonic sensing embodiments illustratedin FIGS. 5-20 such that the photonic catheter has both power transferand sensing capabilities.

The concepts of the present invention may also be utilized in implantedinsulin pumps. Implanted insulin pumps typically consist of two majorsubsystems: a pump assembly for storing and metering insulin into thebody, and a sensor for measuring glucose concentration. The twoassemblies are typically connected by a metallic wire lead encased in abiocompatible catheter. The pump and sensor assemblies are typicallylocated in separate locations within the body to accommodate the largersize of the reservoir and pump assembly (which is typically located inthe gut), and to enable the sensor (typically located near the heart) tomore accurately measure glucose concentration.

The output of the sensor is delivered to the reservoir and pump assemblyas a coded electrical signal where it is used to determine when and howmuch insulin to deliver into the body. The fact that the lead connectingthe two assemblies is a wire lead makes it susceptible to interferencefrom external magnetic fields, particularly the intense magnetic fieldsused in MRI imaging. Interference from MRI fields can induce electricalvoltages in the leads that can damage the pump assembly and causeincorrect operation of the pump which could lead to patient injurypossibly even death.

Induced electrical currents can also cause heating of the lead that canalso damage the pump and cause incorrect operation of the pump andinjury to the patient due to pump failure as well as thermogenic injuryto internal tissues and organs. Shielding of the reservoir and pumpassembly and sensor assembly can reduce direct damage to these devices,but cannot prevent induced electrical voltages and currents frominterfering with and damaging the devices.

According to the concepts of the present invention, a photonic leadreplaces the metallic wire connecting the reservoir and pump assemblyand sensor assembly with a wave-guide such as an optical fiber. Thesensor assembly is also modified to include means to transduce theelectrical signal generated by the sensor into an optical signal that isthen transmitted to reservoir and pump assembly over the wave-guide.This transduction means can be achieved by various combinations ofoptical emitters, optical attenuators, and optical sensors located ineither the sensor assembly or reservoir and pump assembly.

As noted above, the present invention is an implantable device that isimmune or hardened to electromagnetic insult or interference.

In one embodiment of the present invention as illustrated in thefigures, an implantable pacemaker or a cardiac assist system is used toregulate the heartbeat of a patient. The implantable cardiac assistsystem is constructed of a primary device housing that has controlcircuitry therein. This control circuitry may include a control unitsuch a microprocessor or other logic circuits and digital signalprocessing circuits. The primary device housing may also include anoscillator, memory, filtering circuitry, an interface, sensors, a powersupply, and/or a light source.

The microprocessor may be an integrated circuit for controlling theoperations of the cardiac assist system. The microprocessor integratedcircuit can select a mode of operation for the cardiac assist systembased on predetermined sensed parameters. In one embodiment, themicroprocessor integrated circuit isolates physiological signals usingan analog or digital noise filtering circuit.

The primary device housing also can contain circuitry to detect andisolate crosstalk between device pulsing operations and device sensingoperations, a battery power source and a battery power source measuringcircuit. In such an embodiment the microprocessor integrated circuit canautomatically adjust a value for determining an elective replacementindication condition of a battery power source. The value isautomatically adjusted by the microprocessor integrated circuit inresponse to a measured level of a state of the battery power source. Themeasured level is generated by the battery power source measuringcircuit that is connected to the battery power source.

The microprocessor integrated circuit can be programmable from a sourceexternal of the cardiac assist system and can provide physiological orcircuit diagnostics to a source external of the cardiac assist system.

The microprocessor integrated circuit may also include a detectioncircuit to detect a phase timing of an external electromagnetic field.The microprocessor integrated circuit alters its operations to avoidinterfering with the detected external electromagnetic field. Moreover,the cardiac assist system would include sensors may detect a heartsignal and to produce a sensor signal therefrom and a modulator tomodulate the sensor signal to differentiate the sensor signal fromelectromagnetic interference or a sampling circuit to sample the sensorsignal multiple times to differentiate the sensor signal fromelectromagnetic interference, undesirable acoustic signals, large musclecontractions, or extraneous infrared light.

The primary device housing has formed around it, in a preferredembodiment, a shield. The shield can be formed of various compositematerials so as to provide an electromagnetic shield around the primaryhousing. Examples of such materials are metallic shielding or polymer orcarbon composites such as carbon fullerenes. This shield or sheatharound the primary device housing shields the primary device housing andany circuits therein from electromagnetic interference.

The cardiac assist system also includes a lead system to transmit andreceive signals between a heart and the primary device housing. The leadsystem may be a fiber optic based communication system, preferably afiber optic communication system contains at least one channel within amulti-fiber optic bundle, or the lead system may be a plurality ofelectrical leads. The lead system is coated with electromagneticinterference resistant material.

With respect to the electrical lead system, the plurality of electricalleads has a second shielding therearound, the second shieldingpreventing the electrical leads from conducting stray electromagneticinterference. The second shielding can be a metallic sheath to preventthe electrical leads from conducting stray electromagnetic interference;a carbon composite sheath to prevent the electrical leads fromconducting stray electromagnetic interference; or a polymer compositesheath to prevent the electrical leads from conducting strayelectromagnetic interference. The electrical leads may either beunipolar, bipolar or a combination of the two. Moreover, the lead systemitself may be a combination of fiber optic leads and electrical leadswherein these electrical leads can be either unipolar, bipolar or acombination of the two.

The lead systems may include a sensing and stimulation system at anepicardial-lead interface with a desired anatomical cardiac tissueregion. The sensing and stimulation system may include optical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region and/or electrical sensing components to detectphysiological signals from the desired anatomical cardiac tissue region.The sensing and stimulation system may also include optical pulsingcomponents to deliver a stimulus of a predetermined duration and powerto the desired anatomical cardiac tissue region and/or electricalpulsing components to deliver a stimulus of a predetermined duration andpower to the desired anatomical cardiac tissue region. The sensing andstimulation system may also include hydrostatic pressure sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

Although the leads may be fiber optic strands or electrical leads withproper shielding, the actual interface to the tissue, the electrodes,cannot be shielded because the tissue needs to receive the stimulationfrom the device without interference. This causes the electrodes to besusceptible to electromagnetic interference or insult, and such insultcan cause either damage to the tissue area or the circuitry at the otherend. To realize immunity from the electromagnetic interference orinsult, each electrode has an anti-antenna geometrical shape. Theanti-antenna geometrical shape prevents the electrode from picking upand conducting stray electromagnetic interference.

Moreover, the primary device housing, may include for redundancyfiltering circuits as the ends of the electrical leads at the primaryhousing interface to remove stray electromagnetic interference from asignal being received from the electrical lead. The filters may becapacitive and inductive filter elements adapted to filter outpredetermined frequencies of electromagnetic interference.

In addition to the electromagnetic interference shielding, the primarydevice housing, and lead system, whether it is a fiber optic system orelectrical lead system can be coated with a biocompatible material. Sucha biocompatible material is preferably a non-permeable diffusionresistant biocompatible material.

In another embodiment of the present invention as illustrated in thefigures, an implantable pacemaker or a cardiac assist system is used toregulate the heartbeat of a patient. The implantable cardiac assistsystem is constructed of a primary device housing that has controlcircuitry therein. This control circuitry may include a control unitsuch a microprocessor or other logic circuits and digital signalprocessing circuits. The primary device housing may also include anoscillator, memory, filtering circuitry, an interface, sensors, a powersupply, and/or a light source. In a preferred embodiment, the controlcircuitry including the oscillator and an amplifier operate at anamplitude level above that of an induced signal from amagnetic-resonance imaging field.

The microprocessor may be an integrated circuit for controlling theoperations of the cardiac assist system. The microprocessor integratedcircuit can select a mode of operation for the cardiac assist systembased on predetermined sensed parameters. In one embodiment, themicroprocessor integrated circuit isolates physiological signals usingan analog or digital noise filtering circuit.

The primary device housing also can contain circuitry to detect andisolate crosstalk between device pulsing operations and device sensingoperations, a battery power source and a battery power source measuringcircuit. In such an embodiment the microprocessor integrated circuit canautomatically adjust a value for determining an elective replacementindication condition of a battery power source. The value isautomatically adjusted by the microprocessor integrated circuit inresponse to a measured level of a state of the battery power source. Themeasured level is generated by the battery power source measuringcircuit that is connected to the battery power source.

The microprocessor integrated circuit can be programmable from a sourceexternal of the cardiac assist system and can provide physiological orcircuit diagnostics to a source external of the cardiac assist system.

The cardiac assist system also includes a lead system to transmit andreceive signals between a heart and the primary device housing. The leadsystem may be a fiber optic based communication system, preferably afiber optic communication system contains at least one channel within amulti-fiber optic bundle, or the lead system may be a plurality ofelectrical leads. The lead system is coated with electromagneticinterference resistant material.

The cardiac assist system further includes a detection circuit. Thedetection circuit is located in the primary device housing and detectsan electromagnetic interference insult upon the cardiac assist system.Examples of such detection circuits are a thermistor heat detector; ahigh frequency interference detector; a high voltage detector; and/or anexcess current detector. The control circuit places the cardiac assistsystem in an asynchronous mode upon detection of the electromagneticinterference insult by the detection system.

With respect to the electrical lead system, the plurality of electricalleads has a second shielding therearound, the second shieldingpreventing the electrical leads from conducting stray electromagneticinterference. The second shielding can be a metallic sheath to preventthe electrical leads from conducting stray electromagnetic interference;a carbon composite sheath to prevent the electrical leads fromconducting stray electromagnetic interference; or a polymer compositesheath to prevent the electrical leads from conducting strayelectromagnetic interference. The electrical leads may either beunipolar, bipolar or a combination of the two. Moreover, the lead systemitself may be a combination of fiber optic leads and electrical leadswherein these electrical leads can be either unipolar, bipolar or acombination of the two.

The lead systems may include a sensing and stimulation system at anepicardial-lead interface with a desired anatomical cardiac tissueregion. The sensing and stimulation system may include optical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region and/or electrical sensing components to detectphysiological signals from the desired anatomical cardiac tissue region.The sensing and stimulation system may also include optical pulsingcomponents to deliver a stimulus of a predetermined duration and powerto the desired anatomical cardiac tissue region and/or electricalpulsing components to deliver a stimulus of a predetermined duration andpower to the desired anatomical cardiac tissue region. The sensing andstimulation system may also include hydrostatic pressure sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

Although the leads may be fiber optic strands or electrical leads withproper shielding, the actual interface to the tissue, the electrodes,cannot be shielded because the tissue needs to receive the stimulationfrom the device without interference. This causes the electrodes to besusceptible to electromagnetic interference or insult, and such insultcan cause either damage to the tissue area or the circuitry at the otherend. To realize immunity from the electromagnetic interference orinsult, each electrode has an anti-antenna geometrical shape. Theanti-antenna geometrical shape prevents the electrode from picking upand conducting stray electromagnetic interference.

Moreover, the primary device housing, may include for redundancyfiltering circuits as the ends of the electrical leads at the primaryhousing interface to remove stray electromagnetic interference from asignal being received from the electrical lead. The filters may becapacitive and inductive filter elements adapted to filter outpredetermined frequencies of electromagnetic interference.

The primary device housing has formed around it, in a preferredembodiment, a shield. The shield can be formed of various compositematerials so as to provide an electromagnetic shield around the primaryhousing. Examples of such materials are metallic shielding or polymer orcarbon composites such as carbon fullerenes. This shield or sheatharound the primary device housing shields the primary device housing andany circuits therein from electromagnetic interference.

In addition to the electromagnetic interference shielding, the primarydevice housing, and lead system, whether it is a fiber optic system orelectrical lead system can be coated with a biocompatible material. Sucha biocompatible material is preferably a non-permeable diffusionresistant biocompatible material.

In a third embodiment of the present invention as illustrated in thefigures, a cardiac assist system includes a primary device housing. Theprimary device housing has a control circuit, therein, to performsynchronous cardiac assist operations. The cardiac assist system furtherincludes a secondary device housing that has a control circuit, therein,to perform asynchronous cardiac assist operations

A detection circuit, located in either the primary or secondary devicehousing and communicatively coupled to the control circuits, detects anelectromagnetic interference insult upon the cardiac assist system. Thedetection circuit can also be located in a third device housing.Examples of such detection circuits are a thermistor heat detector; ahigh frequency interference detector; a high voltage detector; and/or anexcess current detector.

The detection circuit is communicatively coupled to the control circuitsthrough a fiber optic communication system and/or throughelectromagnetic interference shielded electrical leads. The fiber opticcommunication system or the electromagnetic interference shieldedelectrical leads are coated with a biocompatible material.

The control circuit of the primary device housing terminates synchronouscardiac assist operations and the control circuit of the secondarydevice housing initiates asynchronous cardiac assist operations upondetection of the electromagnetic interference insult by the detectionsystem. In this system the control circuit of the secondary devicehousing places the cardiac assist system in the asynchronous mode for aduration of the electromagnetic interference insult and terminates theasynchronous mode of the cardiac assist system upon detection of anabsence of an electromagnetic interference insult by the detectionsystem. The control circuit of the primary device housing terminates thesynchronous mode of the cardiac assist system for the duration of theelectromagnetic interference insult and re-initiates the synchronousmode of the cardiac assist system upon detection of an absence of anelectromagnetic interference insult by the detection system.

The primary and secondary device housings have formed around them, in apreferred embodiment, a shield. The shield can be formed of variouscomposite materials so as to provide an electromagnetic shield aroundthe primary housing. Examples of such materials are metallic shieldingor polymer or carbon composites such as carbon fullerenes. This shieldor sheath around the primary device housing shields the primary devicehousing and any circuits therein from electromagnetic interference.

In addition to the electromagnetic interference shielding, the primaryand secondary device housings are coated with a biocompatible material.Such a biocompatible material is preferably a non-permeable diffusionresistant biocompatible material.

The cardiac assist system also includes a lead system to transmit andreceive signals between heart and the primary and secondary devicehousings. The lead system may be a fiber optic based communicationsystem, preferably a fiber optic communication system contains at leastone channel within a multi-fiber optic bundle, or the lead system may bea plurality of electrical leads. The lead system is coated withelectromagnetic interference resistant material.

With respect to the electrical lead system, the plurality of electricalleads has a second shielding therearound, the second shieldingpreventing the electrical leads from conducting stray electromagneticinterference. The second shielding can be a metallic sheath to preventthe electrical leads from conducting stray electromagnetic interference;a carbon composite sheath to prevent the electrical leads fromconducting stray electromagnetic interference; or a polymer compositesheath to prevent the electrical leads from conducting strayelectromagnetic interference. The electrical leads may either beunipolar, bipolar or a combination of the two. Moreover, the lead systemitself may be a combination of fiber optic leads and electrical leadswherein these electrical leads can be either unipolar, bipolar or acombination of the two.

The lead systems may include a sensing and stimulation system at anepicardial-lead interface with a desired anatomical cardiac tissueregion. The sensing and stimulation system may include optical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region and/or electrical sensing components to detectphysiological signals from the desired anatomical cardiac tissue region.The sensing and stimulation system may also include optical pulsingcomponents to deliver a stimulus of a predetermined duration and powerto the desired anatomical cardiac tissue region and/or electricalpulsing components to deliver a stimulus of a predetermined duration andpower to the desired anatomical cardiac tissue region. The sensing andstimulation system may also include hydrostatic pressure sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

Although the leads may be fiber optic strands or electrical leads withproper shielding, the actual interface to the tissue, the electrodes,cannot be shielded because the tissue needs to receive the stimulationfrom the device without interference. This causes the electrodes to besusceptible to electromagnetic interference or insult, and such insultcan cause either damage to the tissue area or the circuitry at the otherend. To realize immunity from the electromagnetic interference orinsult, each electrode has an anti-antenna geometrical shape. Theanti-antenna geometrical shape prevents the electrode from picking upand conducting stray electromagnetic interference.

In a fourth embodiment of the present invention, an implantablepacemaker or a cardiac assist system is used to regulate the heartbeatof a patient. The implantable cardiac assist system is constructed of aprimary device housing that has control circuitry therein. This controlcircuitry may include a control unit such a microprocessor or otherlogic circuits and digital signal processing circuits. The primarydevice housing may also include an oscillator, memory, filteringcircuitry, an interface, sensors, a power supply, and/or a light source.

The microprocessor may be an integrated circuit for controlling theoperations of the cardiac assist system. The microprocessor integratedcircuit can select a mode of operation for the cardiac assist systembased on predetermined sensed parameters. In one embodiment, themicroprocessor integrated circuit isolates physiological signals usingan analog or digital noise filtering circuit.

The primary device housing also can contain circuitry to detect andisolate crosstalk between device pulsing operations and device sensingoperations, a battery power source and a battery power source measuringcircuit. In such an embodiment the microprocessor integrated circuit canautomatically adjust a value for determining an elective replacementindication condition of a battery power source. The value isautomatically adjusted by the microprocessor integrated circuit inresponse to a measured level of a state of the battery power source. Themeasured level is generated by the battery power source measuringcircuit that is connected to the battery power source.

The microprocessor integrated circuit can be programmable from a sourceexternal of the cardiac assist system and can provide physiological orcircuit diagnostics to a source external of the cardiac assist system.

The microprocessor integrated circuit may also include a detectioncircuit to detect a phase timing of an external electromagnetic field.The microprocessor integrated circuit alters its operations to avoidinterfering with the detected external electromagnetic field. Moreover,the cardiac assist system would include sensors may detect a heartsignal and to produce a sensor signal therefrom and a modulator tomodulate the sensor signal to differentiate the sensor signal fromelectromagnetic interference or a sampling circuit to sample the sensorsignal multiple times to differentiate the sensor signal fromelectromagnetic interference, undesirable acoustic signals, large musclecontractions, or extraneous infrared light.

The primary device housing has formed around it, in a preferredembodiment, a shield. The shield can be formed of various compositematerials so as to provide an electromagnetic shield around the primaryhousing. Examples of such materials are metallic shielding or polymer orcarbon composites such as carbon fullerenes. This shield or sheatharound the primary device housing shields the primary device housing andany circuits therein from electromagnetic interference.

The cardiac assist system also includes a fiber optic lead system totransmit and receive signals between a heart and the primary devicehousing. The fiber optic communication system preferably contains atleast one channel within a multi-fiber optic bundle. The lead system canbe coated with electromagnetic interference resistant material.

The optic fiber lead systems may include a sensing and stimulationsystem at an epicardial-lead interface with a desired anatomical cardiactissue region. The sensing and stimulation system may include opticalsensing components to detect physiological signals from the desiredanatomical cardiac tissue region and/or electrical sensing components todetect physiological signals from the desired anatomical cardiac tissueregion (in the electrical sensing components, electrical pulses areconverted to light pulses before being transmitted over the leadsystem). The sensing and stimulation system may also include opticalpulsing components to deliver a stimulus of a predetermined duration andpower to the desired anatomical cardiac tissue region and/or electricalpulsing components to deliver a stimulus of a predetermined duration andpower to the desired anatomical cardiac tissue region (in the electricaldelivering components, light pulses are converted to electrical pulsesafter the light pulses are received from the lead system). The sensingand stimulation system may also include hydrostatic pressure sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

Although the leads are fiber optic strands, the actual interface to thetissue, the electrodes, cannot be fiber optics because the tissue needsto receive electrical stimulation from the device. This causes theelectrodes to be susceptible to electromagnetic interference or insult,and such insult can cause either damage to the tissue area or thecircuitry at the other end. To realize immunity from the electromagneticinterference or insult, each electrode has an anti-antenna geometricalshape. The anti-antenna geometrical shape prevents the electrode frompicking up and conducting stray electromagnetic interference.

In addition, the primary device housing and the fiber optic lead systemare coated with a biocompatible material. Such a biocompatible materialis preferably a non-penneable diffusion resistant biocompatiblematerial. The primary device housing further includes an electronicsignal generator and a controlled laser light pulse generator linked tothe electronic signal generator. A fiber optic light pipe for receivesthe laser light pulse from the controlled laser light pulse generator ata proximal end of the fiber optic light pipe. A photodiode, at a distalend of the fiber optic light pipe converts the laser light pulse backinto an electrical pulse. The electrical pulse drives the cardiacelectrodes coupled to the photodiode and to a cardiac muscle.

In a fifth embodiment of the present invention as illustrated in thefigures, an implantable cable for transmission of a signal to and from abody tissue of a vertebrate is constructed of a fiber optic bundlehaving a cylindrical surface of non-immunogenic, physiologicallycompatible material. The fiber optic bundle is capable of beingpermanently implanted in a body cavity or subcutaneously. An opticalfiber in the fiber optic bundle has a distal end for implantation at oradjacent to the body tissue and a proximal end. The proximal end isadapted to couple to and direct an optical signal source. The distal endis adapted to couple to an optical stimulator. The optical fiberdelivers an optical signal intended to cause the optical stimulatorlocated at a distal end to deliver an excitatory stimulus to a selectedbody tissue. The stimulus causes the selected body tissue to function asdesired.

The optical stimulator is constructed, in a preferred embodiment, isconstructed of a photoresponsive device for converting the lightreceived from the optical signal source into electrical energy and forsensing variations in the light energy to produce control signals. Acharge-accumulating device, such as a CCD, receives and stores theelectrical energy produced by the photoresponsive device. A dischargecontrol device, responsive to the control signals, directs the storedelectrical energy from the charge-accumulating device to the cardiacassist device associated with the heart.

A second optical fiber has a distal end coupled to a sensor and aproximal end coupled to a device responsive to an optical signaldelivered by the second optical fiber. The sensor generates an opticalsignal to represent a state of a function of the selected body tissue toprovide feedback to affect the activity of the optical signal source.

In a sixth embodiment of the present invention, an implantable photoniccable system is constructed from a photonic cable, a light source and alight detector. The light source and the light detector form an opticalsensor unit. The photonic cable, in this embodiment, receives signalsfrom a selected tissue area and delivering signals to the selectedtissue area. The system further includes transducers.

The light source illuminates a tissue area, and the light detectordetects properties of the tissue by measuring the output of the lightsignals reflective from the tissue area. A hollow porous cylinder isused to attach the optical sensor unit to the tissue area. Preferably,the light source is a light emitting diode and the light detector is aphotodiode comprising multiple channels. The multiple channels detectlight emission at multiple wavelengths. Moreover, the optical sensorunit includes either a pressure-optical transducer or a reflectiveelement mechanically driven by a moving part of the selected bodytissue.

In a seventh embodiment of the present invention, a cardiac assistsystem is constructed of a primary device housing having a controlcircuit therein. A shielding is formed around the primary device housingto shield the primary device housing and any circuits therein fromelectromagnetic interference. A lead system to transmit and receivesignals between a heart and the primary device housing. A switch placesthe control circuitry into a fixed-rate mode of operation. A changingmagnetic field sensor to sense a change in magnetic field around theprimary housing. The switch places the control circuitry into afixed-rate mode of operation when the changing magnetic field sensorsenses a predetermined encoded changing magnetic field.

In another embodiment of the present invention, a method prevents acardiac assist system from failing during magnetic resonance imaging. Amagnetic-resonance imaging system determines a quiet period for acardiac assist system. Upon making this determination, themagnetic-resonance imaging system locks the timing of a magneticresonance imaging pulse to occur during a quiet period of the cardiacassist system.

In an eighth embodiment of the present invention, a cardiac assistsystem is constructed of a primary device housing having a controlcircuit therein. A shielding is formed around the primary device housingto shield the primary device housing and any circuits therein fromelectromagnetic interference. A lead system to transmit and receivesignals between a heart and the primary device housing. A switch placesthe control circuitry into a fixed-rate mode of operation. An acousticsensor senses a predetermined acoustic signal, and the switch places thecontrol circuitry into a fixed-rate mode of operation when the acousticsensor senses the predetermined acoustic signal.

In a ninth embodiment of the present invention, a cardiac assist systemis constructed of a primary device housing having a control circuittherein. A shielding is formed around the primary device housing toshield the primary device housing and any circuits therein fromelectromagnetic interference. A lead system to transmit and receivesignals between a heart and the primary device housing. A switch placesthe control circuitry into a fixed-rate mode of operation. A nearinfrared sensor senses a predetermined near infrared signal. The switchplaces the control circuitry into a fixed-rate mode of operation whenthe near infrared sensor senses the predetermined near infrared signal.

The present invention also contemplates an electromagnetic radiationimmune tissue invasive stimulation system that includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength; a wave-guide between the proximal end and distal end of thephotonic lead; a distal sensor, in the distal end of the photonic lead,to convert the first light into electrical energy into control signals;an electrical energy storage device to store electrical energy; and acontrol circuit, in response to the control signals, to cause a portionof the stored electrical energy to be delivered to a predeterminedtissue region. In this embodiment, the predetermined tissue region maybe, for example, a region of the spinal cord, a region of the brain, aregion associated with a deep brain structure, the vagal nerve,peripheral nerves that innervate muscles, sacral nerve roots to elicitfunctional contraction of muscles innervated by the sacral nerve roots,sacral nerve roots associated with bladder function, a region of thecochlea, a region of the stomach, or the hypoglossal nerve.

The present invention also contemplates an electromagnetic radiationimmune tissue invasive sensing system that includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength; a wave-guide between the proximal end and distal end of thephotonic lead; a distal sensor, in the distal end of the photonic lead,to convert the first light into electrical energy into control signals;an electrical energy storage device to store electrical energy; and abio-sensor, in the distal end of the photonic lead, to sense acharacteristic of a predetermined tissue region. The light source, inthe proximal end of the photonic lead, produces a second light having asecond wavelength. The distal sensor, in the distal end of the photoniclead and responsive to the bio-sensor, reflects the second light backthe proximal end of the photonic lead such that a characteristic of thesecond light is modulated to encode the sensed characteristic of thepredetermined tissue region. In this embodiment, the sensedcharacteristic may be, for example, an ECG, an EKG, an esophageal ECG, alevel of oxygen, blood pressure, intracranial pressure, or temperature.

The present invention also contemplates an electromagnetic radiationimmune sensing system that includes a photonic lead having a proximalend and a distal end; a light source, in the proximal end of thephotonic lead, to produce a first light having a first wavelength and asecond light having a second wavelength; a wave-guide between theproximal end and distal end of the photonic lead; a bio-sensor, in thedistal end of the photonic lead, to measure changes in an electric fieldlocated outside a body, the electric field being generated by theshifting voltages on a body's skin surface; and a distal sensor, in thedistal end of the photonic lead, to convert the first light intoelectrical energy and, responsive to the bio-sensor, to reflect thesecond light back the proximal end of the photonic lead such that acharacteristic of the second light is modulated to encode the measuredchanges in the electric field. In this embodiment, the measured electricfield may correspond to an ECG signal. Also in this embodiment, thebio-sensor has impedance higher than an impedance of an air gap betweenthe bio-sensor and the body.

While various examples and embodiments of the present invention havebeen shown and described, it will be appreciated by those skilled in theart that the spirit and scope of the present invention are not limitedto the specific description and drawings herein, but extend to variousmodifications and changes all as set forth in the following claims.

What is claimed is:
 1. A cardiac assist device, comprising: a primarydevice housing; said primary device housing having a control circuittherein; a shielding formed around said primary device housing to shieldsaid primary device housing and any circuits therein fromelectromagnetic interference; a lead system to transmit and receivesignals between a selected cardiac tissue region and said primary devicehousing; a switch to place the control circuitry into a fixed-rate modeof operation; an acoustic sensor to sense a predetermined acousticsignal; said switch placing the control circuitry into a fixed-rate modeof operation when said acoustic sensor senses the predetermined acousticsignal; said lead system being a photonic lead system to transmitbetween said primary device housing and the selected cardiac tissueregion, both power and control signals in the form of light; aphotoresponsive device to convert the light transmitted by said photoniclead system into electrical energy and to sense variations in the lightenergy to produce control signals; a charge accumulating device toreceive and store the electrical energy produced by said photoresponsivedevice; and a discharge control device, responsive to the controlsignals, to direct the stored electrical energy from said chargeaccumulating device to the selected cardiac tissue region.
 2. Thecardiac assist device as claimed in claim 1, wherein said shielding is ametallic sheath to shield said primary device housing and any circuitstherein from electromagnetic interference.
 3. The cardiac assist deviceas claimed in claim 1, wherein said shielding is a carbon compositesheath to shield said primary device housing and any circuits thereinfrom electromagnetic interference.
 4. The cardiac assist device asclaimed in claim 1, wherein said shielding is a polymer composite sheathto shield said primary device housing and any circuits therein fromelectromagnetic interference.
 5. The cardiac assist device as claimed inclaim 1, wherein said lead system comprises a fiber optic basedcommunication system.
 6. The cardiac assist device as claimed in claim5, wherein said fiber optic communication system contains at least onechannel within a multi-fiber optic bundle.
 7. The cardiac assist deviceas claimed in claim 5, wherein said fiber optic based communicationsystem is covered with a biocompatible material.
 8. The cardiac assistdevice as claimed in claim 6, wherein said multi-fiber optic bundle iscovered with a biocompatible material.
 9. The cardiac assist device asclaimed in claim 1, wherein said lead system comprises a plurality ofelectrical leads.
 10. The cardiac assist device as claimed in claim 9,wherein said plurality of electrical leads have a second shieldingtherearound, said second shielding preventing said electrical leads fromconducting stray electromagnetic interference.
 11. The cardiac assistdevice as claimed in claim 10, wherein said second shielding is ametallic sheath to prevent said electrical leads from conducting strayelectromagnetic interference.
 12. The cardiac assist device as claimedin claim 10, wherein said second shielding is a carbon composite sheathto prevent said electrical leads from conducting stray electromagneticinterference.
 13. The cardiac assist device as claimed in claim 10,wherein said second shielding is a polymer composite sheath to preventsaid electrical leads from conducting stray electromagneticinterference.
 14. The cardiac assist device as claimed in claim 9,wherein each electrical lead includes an electrical filter, saidelectrical filter removing stray electromagnetic interference from asignal being received from said electrical lead.
 15. The cardiac assistdevice as claimed in claim 14, wherein said plurality of electricalleads have a second shielding therearound, said second shieldingpreventing said electrical leads from conducting stray electromagneticinterference.
 16. The cardiac assist device as claimed in claim 15,wherein said second shielding is a carbon composite sheath to preventsaid electrical leads from conducting stray electromagneticinterference.
 17. The cardiac assist device as claimed in claim 15,wherein said second shielding is a polymer composite sheath to preventsaid electrical leads from conducting stray electromagneticinterference.
 18. The cardiac assist device as claimed in claim 1,wherein said shielding is covered with a biocompatible material.
 19. Thecardiac assist device as claimed in claim 1, wherein said primary devicehousing includes a microprocessor integrated circuit for controlling theoperations of the cardiac assist device.
 20. The cardiac assist deviceas claimed in claim 19, further comprising a battery power source and abattery power source measuring circuit; said microprocessor integratedcircuit automatically adjusting a value for determining an electivereplacement indication condition of a battery power source such that thevalue is automatically adjusted by said microprocessor integratedcircuit in response to a measured level of a state of said battery powersource, the measured level generated by said battery power sourcemeasuring circuit connected to said battery power source.
 21. Thecardiac assist device as claimed in claim 19, wherein saidmicroprocessor integrated circuit isolates physiological signals using anoise filtering circuit.
 22. The cardiac assist device as claimed inclaim 19, wherein said microprocessor integrated circuit isolatesphysiological signals using digital noise filtering.
 23. The cardiacassist device as claimed in claim 19, wherein said microprocessorintegrated circuit is programmable from a source external of the cardiacassist device.
 24. The cardiac assist device as claimed in claim 19,wherein said microprocessor integrated circuit provides physiologicaldiagnostics to a source external of the cardiac assist device.
 25. Thecardiac assist device as claimed in claim 19, wherein saidmicroprocessor integrated circuit provides circuit diagnostics to asource external of the cardiac assist device.
 26. The cardiac assistdevice as claimed in claim 19, wherein said microprocessor integratedcircuit is programmable from a source external of the cardiac assistdevice and provides circuit diagnostics to a source external of thecardiac assist device.
 27. The cardiac assist device as claimed in claim1, wherein said leads system is a combination of a fiber optic basedcommunication system and electrical leads.
 28. The cardiac assist deviceas claimed in claim 27, wherein said fiber optic communication systemcontains at least one channel within a multi-fiber optic bundle.
 29. Thecardiac assist device as claimed in claim 1, wherein said lead systemincludes a sensing and stimulation system at an interface with theselected cardiac tissue region.
 30. The cardiac assist device as claimedin claim 29, wherein said sensing and stimulation system includesoptical sensing components to detect physiological signals from theselected cardiac tissue region.
 31. The cardiac assist device as claimedin claim 30, wherein said sensing and stimulation system includesoptical pulsing components to deliver a stimulus of a predeterminedduration and power to the selected cardiac tissue region.
 32. Thecardiac assist device as claimed in claim 30, wherein said sensing andstimulation system includes optical pulsing components to deliver astimulus of a predetermined duration and power to the selected cardiactissue region and electrical pulsing components to deliver a stimulus ofa predetermined duration and power to the selected cardiac tissueregion.
 33. The cardiac assist device as claimed in claim 29, whereinsaid sensing and stimulation system includes optical sensing componentsto detect physiological signals from the desired anatomical cardiactissue region and electrical sensing components to detect physiologicalsignals from the selected cardiac tissue region.
 34. The cardiac assistdevice as claimed in claim 29, wherein said sensing and stimulationsystem includes electrical sensing components to detect physiologicalsignals from the selected cardiac tissue region.
 35. The cardiac assistdevice as claimed in claim 29, wherein said sensing and stimulationsystem includes optical pulsing components to deliver a stimulus of apredetermined duration and power to the selected cardiac tissue region.36. The cardiac assist device as claimed in claim 29, wherein saidsensing and stimulation system includes optical pulsing components todeliver a stimulus of a predetermined duration and power to the selectedcardiac tissue region and electrical pulsing components to deliver astimulus of a predetermined duration and power to the selected cardiactissue region.
 37. The cardiac assist system as claimed in claim 1,wherein said photoresponsive device is a small surface area photodiodeand a large surface area photodiode, said small surface area photodiodesensing variations in the light energy to produce control signals, saidlarge surface area photodiode converting the light transmitted by saidphotonic lead system into electrical energy.
 38. The cardiac assistsystem as claimed in claim 1, wherein said photoresponsive device is anarray of photodiodes having a first section of photodiodes and a secondsection of photodiodes, said first section of photodiodes sensingvariations in the light energy to produce control signals, said secondsection of photodiodes converting the light transmitted by said photoniclead system into electrical energy.
 39. The cardiac assist system asclaimed in claim 1, wherein said photoresponsive device includes acharge transfer control circuit and a photodiode, said charge transfercontrol circuit controlling a discharging of a photodiode capacitance intwo separate discharge periods during an integration period of thephotodiode such that a first discharge period of the photodiodecapacitance provides the sensing of variations in the light energy toproduce control signals and a second discharge period of the photodiodecapacitance provides the converting the light transmitted by saidphotonic lead system into electrical energy.
 40. The cardiac assistsystem as claimed in claim 39, wherein the first discharge period iscompleted before the second discharge period.
 41. The cardiac assistsystem as claimed in claim 39, wherein the first discharge period is ashorter time duration that the time duration of the second dischargeperiod.
 42. The cardiac assist system as claimed in claim 39, whereinthe integration period corresponds to the sampling period of the lightto derive control data.
 43. The cardiac assist system as claimed inclaim 39, wherein during the first discharge period, a control signalsensing circuit is connected to said photodiode, and during the seconddischarge period, said charge accumulating device is connected to saidphotodiode.
 44. The cardiac assist system as claimed in claim 1, whereinsaid charge accumulating device is a capacitor.
 45. The cardiac assistsystem as claimed in claim 1, wherein said charge accumulating device isa rechargeable battery.
 46. The cardiac assist system as claimed inclaim 1, wherein said discharge control device is a controllable switch.47. The cardiac assist system as claimed in claim 1, wherein said switchis a reed switch.
 48. The cardiac assist system as claimed in claim 1,wherein said switch is a solid-state switch.
 49. A cardiac assistdevice, comprising: a primary device housing; said primary devicehousing having a control circuit therein; a shielding formed around saidprimary device housing to shield said primary device housing and anycircuits therein from electromagnetic interference; a lead system totransmit and receive signals between a selected cardiac tissue regionand said primary device housing; a switch to place the control circuitryinto a fixed-rate mode of operation; an acoustic sensor to sense apredetermined acoustic signal; said switch placing the control circuitryinto a fixed-rate mode of operation when said acoustic sensor senses thepredetermined acoustic signal; a detection circuit to detect a phasetiming of an external electromagnetic field; and said control circuitaltering its operations to avoid interfering with the detected externalelectromagnetic field.
 50. A cardiac assist system, comprising: aprimary device housing; said primary device housing having a controlcircuit therein; a shielding formed around said primary device housingto shield said primary device housing and any circuits therein fromelectromagnetic interference; a lead system to transmit and receivesignals between a selected cardiac tissue region and said primary devicehousing; a switch to place the control circuitry into a fixed-rate modeof operation; a near infrared sensor to sense a predetermined nearinfrared signal; said switch placing the control circuitry into afixed-rate mode of operation when said near infrared sensor senses thepredetermined near infrared signal.
 51. The cardiac assist device asclaimed in claim 50, wherein said shielding is a metallic sheath toshield said primary device housing and any circuits therein fromelectromagnetic interference.
 52. The cardiac assist device as claimedin claim 50, wherein said shielding is a carbon composite sheath toshield said primary device housing and any circuits therein fromelectromagnetic interference.
 53. The cardiac assist device as claimedin claim 50, wherein said shielding is a polymer composite sheath toshield said primary device housing and any circuits therein fromelectromagnetic interference.
 54. The cardiac assist device as claimedin claim 50, wherein said lead system comprises a fiber optic basedcommunication system.
 55. The cardiac assist device as claimed in claim54, wherein said fiber optic communication system contains at least onechannel within a multi-fiber optic bundle.
 56. The cardiac assist deviceas claimed in claim 54, wherein said fiber optic based communicationsystem is covered with a biocompatible material.
 57. The cardiac assistdevice as claimed in claim 55, wherein said multi-fiber optic bundle iscovered with a biocompatible material.
 58. The cardiac assist device asclaimed in claim 50, wherein said lead system comprises a plurality ofelectrical leads.
 59. The cardiac assist device as claimed in claim 58,wherein said plurality of electrical leads have a second shieldingtherearound, said second shielding preventing said electrical leads fromconducting stray electromagnetic interference.
 60. The cardiac assistdevice as claimed in claim 59, wherein said second shielding is ametallic sheath to prevent said electrical leads from conducting strayelectromagnetic interference.
 61. The cardiac assist device as claimedin claim 59, wherein said second shielding is a carbon composite sheathto prevent said electrical leads from conducting stray electromagneticinterference.
 62. The cardiac assist device as claimed in claim 59,wherein said second shielding is a polymer composite sheath to preventsaid electrical leads from conducting stray electromagneticinterference.
 63. The cardiac assist device as claimed in claim 58,wherein each electrical lead includes an electrical filter, saidelectrical filter removing stay electromagnetic interference from asignal being received from said electrical lead.
 64. The cardiac assistdevice as claimed in claim 63, wherein said plurality of electricalleads have a second shielding therearound, said second shieldingpreventing said electrical leads from conducting stray electromagneticinterference.
 65. The cardiac assist device as claimed in claim 64,wherein said second shielding is a carbon composite sheath to preventsaid electrical leads from conducting stray electromagneticinterference.
 66. The cardiac assist device as claimed in claim 64,wherein said second shielding is a polymer composite sheath to preventsaid electrical leads from conducting stray electromagneticinterference.
 67. The cardiac assist device as claimed in claim 50,wherein said shielding is cover with a biocompatible material.
 68. Thecardiac assist device as claimed in claim 50, wherein said primarydevice housing includes a microprocessor integrated circuit forcontrolling the operations of the cardiac assist device.
 69. The cardiacassist device as claimed in claim 68, further comprising a battery powersource and a battery power source measuring circuit; said microprocessorintegrated circuit automatically adjusting a value for determining anelective replacement indication condition of a battery power source suchthat the value is automatically adjusted by said microprocessorintegrated circuit in response to a measured level of a state of saidbattery power source, the measured level generated by said battery powersource measuring circuit connected to said battery power source.
 70. Thecardiac assist device as claimed in claim 68, wherein saidmicroprocessor integrated circuit isolates physiological signals using anoise filtering circuit.
 71. The cardiac assist device as claimed inclaim 68, wherein said microprocessor integrated circuit isolatesphysiological signals using digital noise filtering.
 72. The cardiacassist device as claimed in claim 68, wherein said microprocessorintegrated circuit is programmable from a source external of the cardiacassist device.
 73. The cardiac assist device as claimed in claim 68,wherein said microprocessor integrated circuit provides physiologicaldiagnostics to a source external of the cardiac assist device.
 74. Thecardiac assist device as claimed in claim 68, wherein saidmicroprocessor integrated circuit provides circuit diagnostics to asource external of the cardiac assist device.
 75. The cardiac assistdevice as claimed in claim 68, wherein said microprocessor integratedcircuit is programmable from a source external of the cardiac assistdevice and provides circuit diagnostics to a source external of thecardiac assist device.
 76. The cardiac assist device as claimed in claim50, wherein said leads system is a combination of a fiber optic basedcommunication system and electrical leads.
 77. The cardiac assist deviceas claimed in claim 76, wherein said fiber optic communication systemcontains at least one channel within a multi-fiber optic bundle.
 78. Thecardiac assist device as claimed in claim 76, wherein said sensing andstimulation system includes optical sensing components to detectphysiological signals from the selected cardiac tissue region.
 79. Thecardiac assist device as claimed in claim 78, wherein said sensing andstimulation system includes optical pulsing components to deliver astimulus of a predetermined duration and power to the selected cardiactissue region.
 80. The cardiac assist device as claimed in claim 78,wherein said sensing and stimulation system includes optical pulsingcomponents to deliver a stimulus of a predetermined duration and powerto the selected cardiac tissue region and electrical pulsing componentsto deliver a stimulus of a predetermined duration and power to theselected cardiac tissue region.
 81. The cardiac assist device as claimedin claim 50, wherein said lead system includes a sensing and stimulationsystem at an epicardial-lead interface with the selected cardiac tissueregion.
 82. The cardiac assist device as claimed in claim 77, whereinsaid sensing and stimulation system includes optical sensing componentsto detect physiological signals from the desired anatomical cardiactissue region and electrical sensing components to detect physiologicalsignals from the selected cardiac tissue region.
 83. The cardiac assistdevice as claimed in claim 81, wherein said sensing and stimulationsystem includes electrical sensing components to detect physiologicalsignals from the selected cardiac tissue region.
 84. The cardiac assistdevice as claimed in claim 81, wherein said sensing and stimulationsystem includes optical pulsing components to deliver a stimulus of apredetermined duration and power to the selected cardiac tissue region.85. The cardiac assist device as claimed in claim 81, wherein saidsensing and stimulation system includes optical pulsing components todeliver a stimulus of a predetermined duration and power to the selectedcardiac tissue region and electrical pulsing components to deliver astimulus of a predetermined duration and power to the selected cardiactissue region.
 86. The cardiac assist device as claimed in claim 50,wherein said lead system is a photonic lead system to transmit betweensaid primary device housing and the selected cardiac tissue region, bothpower and control signals in the form of light, and further comprising:a photoresponsive device to convert the light transmitted by saidphotonic lead system into electrical energy and to sense variations inthe light energy to produce control signals; a charge accumulatingdevice to receive and store the electrical energy produced by saidphotoresponsive device; and a discharge control device, responsive tothe control signals, to direct the stored electrical energy from saidcharge accumulating device to the selected cardiac tissue region. 87.The cardiac assist system as claimed in claim 86, wherein saidphotoresponsive device is a small surface area photodiode and a largesurface area photodiode, said small surface area photodiode sensingvariations in the light energy to produce control signals, said largesurface area photodiode converting the light transmitted by saidphotonic lead system into electrical energy.
 88. The cardiac assistsystem as claimed in claim 86, wherein said photoresponsive device is anarray of photodiodes having a first section of photodiodes and a secondsection of photodiodes, said first section of photodiodes sensingvariations in the light energy to produce control signals, said secondsection of photodiodes converting the light transmitted by said photoniclead system into electrical energy.
 89. The cardiac assist system asclaimed in claim 86, wherein said photoresponsive device includes acharge transfer control circuit and a photodiode, said charge transfercontrol circuit controlling a discharging of a photodiode capacitance intwo separate discharge periods during an integration period of thephotodiode such that a first discharge period of the photodiodecapacitance provides the sensing of variations in the light energy toproduce control signals and a second discharge period of the photodiodecapacitance provides the converting the light transmitted by saidphotonic lead system into electrical energy.
 90. The cardiac assistsystem as claimed in claim 89, wherein the first discharge period iscompleted before the second discharge period.
 91. The cardiac assistsystem as claimed in claim 89, wherein the first discharge period is ashorter time duration that the time duration of the second dischargeperiod.
 92. The cardiac assist system as claimed in claim 89, whereinthe integration period corresponds to the sampling period of the lightto derive control data.
 93. The cardiac assist system as claimed inclaim 89, wherein during the first discharge period, a control signalsensing circuit is connected to said photodiode, and during the seconddischarge period, said charge accumulating device is connected to saidphotodiode.
 94. The cardiac assist system as claimed in claim 86,wherein said charge accumulating device is a capacitor.
 95. The cardiacassist system as claimed in claim 86, wherein said charge accumulatingdevice is a rechargeable battery.
 96. The cardiac assist system asclaimed in claim 86, wherein said discharge control device is acontrollable switch.
 97. The cardiac assist system as claimed in claim50, further comprising: a detection circuit to detect a phase timing ofan external electromagnetic field; said control circuit altering itsoperations to avoid interfering with the detected externalelectromagnetic field.
 98. The cardiac assist system as claimed in claim50, wherein said switch is a reed switch.
 99. The cardiac assist systemas claimed in claim 50, wherein said switch is a solid-state switch.